Here, we want to calculate the value of x and subsequently get the value of angle A.
To do this, we need to understand the relationship between ∠A and ∠B
Mathematically;
∠A + ∠B = 180 (alternate exterior angles are supplementary)
This means that;
5x - 18 = 3x + 42
Collect like terms
5x-3x = 42 + 18
2x = 60
x = 60/2
x = 30
From the question A = 5x - 18
Thus ∠A = 5(30) - 18
∠A = 150-18
∠A = 132°
Hence ∠A = 132° and x = 30
