求点一下思路就行。。。

1. you have buy three producthowever, the utility of C is the lowest, so you buy one C
2. the 2 dollar for A can get utility 120,
3.buy B until the utility can't reach 120. it's 3
2 A 3B 1C

if you don't need buy C

then
1. buy 3B
2. buy 4A
3. buy 1B
according to choose the max utilty

但是你这样，才花了4B+4A=8+4=12元钱，你还有40块钱没花呢。。

我把12unit 看成total 是52元了 logic 一樣
choose the higher utility
Mua/Pa
Mub/Pb
Muc/Pc
you should calculate that first