3x-5y=11 ------- 1
x=3y+1――――2
from 2 make x subject of the formula
x=3y+1――――3
so put （3y+1）for x in 1
3（3y+1）-5y=11
9y+3-5y=11
4y+3=11
4y=11-3
4y=8
divide both side by 4
y=2――――4
put 2 for y in 3
x=3y+1
x=3（2）+1
x =7
