tolong bantu no 39-40 pake jalan cara cepat plzz besok dikumpul

40. Dadar gulung → x
Roti bolu → y

4x + 3y = 6.400 → ×2
2x + 4y = 5.200 → ×4
_____________
8x + 6y = 12.800
8x + 16y = 20.800
_____________ -
-10y = -8.000
y = -8.000 / -10
y = 800

2x + 4y = 5.200
2x + (4×800) = 5.200
2x + 3.200 = 5.200
2x = 5.200 - 3.200
2x = 2.000
x = 2.000 / 2
x = 1.000

Maka, 10x + 10y
= (10×1.000) + (10×800)
= 10.000 + 8.000
= 18.000 (C)