No 12, gimana ya caranyaa??

Misalkan
1/x = a
1/y = b

Maka
5a + 6b = 3 [×3]
3a + 5b = 6 [×5]

15a + 18b = 9
15a + 25b = 30
_____________ -
-7b = -21
b = -21/-7
b = 3

3a + 5b = 6
3a + 5(3) = 6
3a + 15 = 6
3a = 6 - 15
a = -9/3
a = -3

1/x = a
x = 1/a
x = -1/3

1/y = b
y = 1/b
y = 1/3

x + y
= -1/3 + 1/3
= 0 (C)