answer: he needs 200g of butter
.
.
.
explanation: since he needs 80g of butter to make fish pie for 6 people he would need 160g for 12 people. then you’d have to make for 3 more people which is half of 6 so you would need half the amount of butter for the 3, which is 40g of butter. then you just add up the amount of butter 160+40=200g of butter to make a fish pie for 15 people.