jika y=3x-7 dan 9x+7=11 maka nilai dari x+y adalah

9x-7=11 ---> 9x = 11 + 7
9x = 18
x = 2

y = 3x - 7
y = 3.2 - 7
y = 6 - 7
y = -1

jadi x+y = 2 + (-1)
= 1

y = 3x - 7
-3x + y = -7 |×3| -9x + 3y = -21
9x + 7y = 11 |×1| 9x + 7y = 11
------------------------------------------- +
10y = -10
y = -10/10
y = -1

y = 3x - 7
-1 = 3x - 7
-1 + 7 = 3x
6 = 3x
6/3 = x
2 = x

Maka,
x + y = 2 + (-1) = 1

Semoga membantu dan semoga bermanfaat...