Упростите выражение:
1) -2,4m*(-3n);
2)-8a-12b+5a-17b;
3)a-(a+5)+(-7+a);
4)-5(y-4)+(y-5)

1) -2,4m*(-3n) = 7,2mn

2) -8a-12b+5a-17b = - 8a+5a + (-12b) - 17b = - 3a - 29b

3) a-(a+5)+(-7+a)= a - a- 5 - 7 +a = a - 12

4) - 5(y-4)+(y-5) = - 5y+20 +y - 5 =

-4y+15