tolong bantu ya kak.

jawab

11,

garis melalui (0,30) dan (40, 0)  --> 3x + 4y = 120
garis melalui (0,40) dan (20,0) -->  2x + y = 40
titk potongnya

3x+ 4y = 120
2x + y = 40 ....kali 4

3x + 4y = 120
8x + 4y = 160 ....(-)
-5x = - 40
x = 8 ,
y= 40 - 2x = 40 - 16 = 24

f(x,y) = 3x + 2y
f(8, 24) = 3(8) + 2(24) = 24 + 48 = 72