Question

4x – 7y = –9
x + 3y = 12

Answer 1

4x - 7y = -9 -------- eqn (1)
x + 3y = 12--------eqn (2)

Make x the subject for eqn (2)
x = 12 - 3y --------eqn (3)

Put the answer of x in eqn (3) into anywhere you see x in eqn (1)
4(12 - 3y) -7y = -9

Expand the bracket and solve for y
48 - 12y - 7y = -9
48 - 19y = -9
-19y = -9 - 48
-19y = -57

Divide both sides by -19 to make y stand alone
\[y = \frac{-57}{-19}\]
y = 3

Put the answer for y (y = 3) into eqn (2) above and solve for x
x + 3y = 12
x + 3(3) = 12
x + 9 = 12
Subtract 9 from both sides to allow x to stand alone
x = 12 - 9
x = 3

Hence, x = 3 and y = 3