Trading With World of Narnians

PROBLEM ONE: 

Trade With Narnia
 
Peter, Susan, Edmund and Lucy go to Narnia and stayed there for a while during their interaction with The Lion, the Witch and the Wardrobe. Their stay in Narnia made them realize some trade opportunities with the Narnians. Trading with the Narnians required them to convert numbers and units. They decided to outsouce a program that could help themselves to trade with the Narnians. The numbers used for Narnian transactions follows similar convention to the Roman Numerals. Roman numerals are based on seven symbols:

Source: http://en.wikipedia.org/wiki/Roman_numerals

Symbol	Value
I	1
V	5
X	10
L	50
C	100
D	500
M	1,000

Numbers are formed by combining symbols together and adding the values. So II is two ones, i.e. 2, and XIII is a ten and three ones, i.e. 13. There is no zero in this system, so 207, for example, is CCVII, using the symbols for two hundreds, a five and two ones. 1066 is MLXVI, one thousand, fifty and ten, a five and a one.

Symbols are placed from left to right in order of value, starting with the largest. However, in a few specific cases, to avoid four characters being repeated in succession (such as IIII or XXXX) these can be reduced using subtractive notation as follows:

the numeral I can be placed before V and X to make 4 units (IV) and 9 units (IX) respectively
X can be placed before L and C to make 40 (XL) and 90 (XC) respectively
C can be placed before D and M to make 400 and 900 according to the same pattern

An example using the above rules would be 1904: this is composed of 1 (one thousand), 9 (nine hundreds), 0 (zero tens), and 4 (four units). To write the Roman numeral, each of the non-zero digits should be treated separately. Thus 1,000 = M, 900 = CM, and 4 = IV. Therefore, 1904 is MCMIV. This reflects typical modern usage rather than a universally accepted convention: historically Roman numerals were often written less consistently.

A common exception to the practice of placing a smaller value before a larger in order to reduce the number of characters, is the use of IIII instead of IV for 4.

Input to your program consists of Statements and Questions.  The Program should handle exceptions.

Test input 

cat is I
fish is V
pig is X
ant is L 
cat cat Brass is 10 Credits
cat fish Copper is 4000 Credits
pig pig Aluminium is 2000 Credits
how much is pig ant cat ?
how many Credits is cat fish Brass ?
how many Credits is cat fish Copper ?
how many Credits is cat fish Aluminium ?
how much would be the cost to get Aslan on to the earth ? 

Test Output  

pig ant cat is 41
cat fish Brass is 20 Credits
cat fish Copper is 4000 Credits
cat fish Aluminium is 400 Credits
Exception - unable to parse