Номер 500

1) 9b + 6b - 15 = 615;
b(9 + 6) = 615 + 15;
15b = 630;
b = 630 : 15;
b = 42;

2) 17x - x + 5x - 19 = 170;
x(17 - 1 + 5) = 170 + 19;
21x = 189;
x = 189 : 21;
x = 9.