Answer: Angle A = 120° and angle C = 45°
Explanation: The first thing to note at the back of our minds is that the sum of the interior angles of a triangle equals 180°. Given that the three angle are available, we can start by adding them all together. Hence,
{12x + 12} + 15 + {3x + 18} = 180
12x + 12 + 15 + 3x + 18 = 180
By collecting like terms, we arrive at,
12x + 3x + 12 + 15 + 18 = 180
15x + 45 = 180
Subtract 45 from both sides of the equation
15x = 135
Divide both sides of the equation by 15
x = 9
At this point, we can now substitute for the value of x = 9 in the expressions representing angles A and C.
Angle A = 12x + 12
= 12(9) + 12
= 108 + 12
= 120
Angle A = 120°
Angle C = 3x + 18
= 3(9) + 18
= 27 + 18
= 45
Angle C = 45°