The 3 angles of a triangle need to equal 180 degrees.
Angle B is given as 15, so the sum of angle A and C need to equal 180 - 15 = 165 degrees.
Set up the equation:
(12x+12) + (3x+18) = 165
Combine like terms:
15x + 30 = 165
Subtract 30 from each side:
15x = 135
Divide both sides by 15:
x = 135 /15
x = 9
Now you know X, replace x in each equation and solve:
A = 12x + 12 = 12(9) + 12 = 108 +12 = 120
B = 3x+18 = 3(9) +18 = 27 +18 = 45
Angle A = 120
Angle B = 45
