Ответ:

1) y-3+by-3b

2) 3mn-9n+5m^2-15m

3) 5ax+5ay-bx-by

Объяснение:

1) (y - 3)+b(y - 3) = y-3+by-3b

2) 3n(m-3)+5m(m-3) = 3mn-9n+5m^2-15m

3) 5a(x+y)-b(x+y) = 5ax+5ay-bx-by