Try This, I think it will be helpful.
select
Customer_detail.c_id,
Productdetail.p_id,
Productdetail.pro_name,
Productdetail.rate,
Customer_detail.c_name
from
((saledetail INNER JOIN Productdetail ON saledetail.p_id=Productdetail.p_id)
INNER JOIN Salesbill on Salesbill.s_id=saledetail.s_id)
Inner JOIN Customer_detail on saledetail.c_id=Customer_detail.c_id
where
Salesbill.billno=30;