(m+2)/(m+3) : (5m+10)/(9-m^2) - (2m-1)/15 =
= (m+2)/(m+3)*(3-m)(3+m)/5(m+2) - (2m-1)/15 =
= (3-m)/5 - (2m-1)/15 = [3((3-m) - (2m-1)]/15 = (9-3m-2m+1)/15 =
=(10-5m)/15 = (2-m)/3
Поясняю, в начале решения применила формулу сокращённого умножения: 9-m^2 = (3-m)(3+m)