tolong ya memakai cara

x = 3 & y = 5
ax + by = 29
3a + 5b = 29 ... pers 1

x = 7 & y = - 2
ax + by = 13
7a - 2b = 13 .. pers 2

pers 1 & 2
3a + 5b = 29 |×2
7a - 2b = 13 |×5
maka
6a + 10b = 58
35a - 10b = 65
-----------------------(+)
41a = 123
a = 3

subtitusi
3a + 5b = 29
3(3) + 5b = 29
9 + 5b = 29
5b = 29 - 9
5b = 20
b = 4

nilai a dan b = 3 dan 4 ( A )