-x + 3y = 4 dan 4x + 3y = 29 sehingga ax + by=13 dan ax-by=7 maka 6a-5b=

4x + 3y = 29
-4x + 12y = 16
--------------------- +
15y = 45
y = 3

x = 3y - 4 = 9 - 4 = 5

ax + by = 13 --> 5a + 3b = 13....(3)
ax - by = 7 --> 5a - 3b = 7...(4)

Eliminasi pers 3 & 4 ,didapat :
a = 2
b = 1

Jadi, 6a - 5b = 12 - 5 = 7