mohon di jawab makasih

2x + y = 8...(1)
x + 2y = 7....(2) => x = 7 -2y. subsitusikan ke (1)
2x + y = 8
2(7- 2y) + y = 8
14 -4y + y = 8
- 3y = -6
y = 2
x = 7 - 2.2
x = 7 -4
x = 3
f (x, y) = 4x + 5y
= 4.3 + 5.2
= 12 + 10
= 22