tolong ya kk. terima kasih

jawab

20x + 12y = 240
5x + 3y = 60

15x +18y = 270
5x + 6y = 90

5x + 3y = 60
5x + 6y = 90 ....(-)
-3y = - 30
y=  10

5x + 3y = 60
5x + 30 = 60
5x= 30
x = 6

f(x,y)= 7x +6y = 7(6) +6(10)= 102