Jen and heather went to lunch. when the bill came jen discovered that she had only 8.00 dollars, luckly heather had enough money to pay the other part or 3/5 of the bill.

To answer this question, let's analyze the given problem above.
Given that Heather paid the other part of the bill which is 3/5 of the bill, then this means that, Jen paid only 2/5 of the bill. Now that Jen has only 8 dollars, this 8 dollars is equivalent to 2/5 of the bill. The next thing we are going to find out is how much did Heather pay which is 3/5 of the bill. 
So 2/5 = 8 dollars
     3/5 = ?dollars
Therefore, the answer would be $12. The amount that Heather paid is $12. Hope this answer helps.