a. x^2 + b^2 = c^2
x^2 + 18^2 = 30^2
x^2 + 324 = 900
x^2 = 900 - 324
x^2 = 576
x = sqrt 576
x = 24 <===
b. (2x + 20) + (2x) + (x) + (3x + 20) = 360
8x + 40 = 360
8x = 360 - 40
8x = 320
x = 320/8
x = 40
2x + 20 = 2(40) + 20 = 80 + 20 = 100
2x = 2(40) = 80
3x + 20 = 3(40) + 20 = 120 + 20 = 140