Question 660573
x + y = 21
6x = 27 + 3y : rewrite as 6x - 3y = 27
Multiply the first equation by 3
3(x+y=21)
3x + 3y = 63
Add to the second equation
6x + 3x - 3y + 3y = 27 + 63
9x = 90
9x/9 = 90/9
x = 10
y = 21 - 10 = 11