1)=(-6-7)/(-4+5)= -13/1= -13

2) = (-1.2-7)/(-0.8+5)= -8.2/4.2 = -41/21

3) = (0-7)/(0+5) = -7/5

4) = (7.5-7)/(5+5) = 0.5/10 = 0.05