Answer:
for the third problem a = cb
for the 4th problem x = 5a + g
for the 2nd problem p = (q - 3r) / 4
for the first problem x = (-9 - z) / y
for the last problem: b = 15
A = 1/2 bh
75 = 1/2 b(10)
75 = 1/2 10b
multiply both sides by 2
150 = 10b
divide by 10 from both sides
15 = b
b = 15
