Consider the system of equations. x – 3y = 9 1/5x - 2y = -1

 x – 3y = 9  (1)
1/5x - 2y = -1 (2)

(1):
x - 3y = 9
x = 9 + 3y (1a)

(2):
1/5x - 2y = -1
x - 10y = -5 (2a)

Sub (1a) into (2a):
9 + 3y - 10y = -5
9 - 7y = -5
-7y = -5 - 9
-7y = -14
7y = 14
y = 2 Sub into (1a)

x = 9 + 3y 
x = 9 + 3(2)
x = 9 + 6
x = 15

Ans: x = 15, y = 2

Main idea on left, details on right