Solve simultaneous equations: 3x + y = 12 and 5x + 5y = 30

Make y the subject of equation 1 by subtracting 3x from both sidesy = 12 - 3x
Substitute 12 - 3x for y in equation 25x + 5(12 - 3x) = 305x + 512 - 53x = 305x + 60 -15x = 3060 - 10x = 30 # add 5x and -15x
Solve60 = 30 + 10x # add 13x to both sides30 = 10x # minus 30 from both sides3 = x # divide both sides by 10
Answer: x = 3