1) 9b + 6b - 15 = 615
15b = 615 + 15
15b = 630
b = 630 / 15
b = 42
9 * 42 + 6 * 42 - 15 = 615
2) 2a + 123a + 97 = 472
125a = 472 - 97
125a = 375
a = 375 / 125
a = 3
2 * 3 + 123 * 3 + 97 = 472
3) 17x - x + 5x - 19 = 170
21x - 19 = 170
21x = 170 + 19
21x = 189
x = 189 / 21
x = 9
17 * 9 - 9 + 5 * 9 - 19 = 170
4) 73y - y - 22y + 40 = 190
50y + 40 = 190
50y = 190 - 40
50y = 150
y = 150 / 50
y = 3
73 * 3 - 3 - 22 * 3 + 40 = 190