Subtracting integers! what is (-10) - 9?

If a =6, what is the value of 2a(3b + 5c)?

What is the effect on the graph of the function f(x)=x when f(x) is replaced with -f(x)+4

Astudent draws two parabolas both parabolas cross the x axis at (-4,0) and (6,0) the y intercept of the first parabolas is (0,-12). the y intercept of the second parabola is (0,-24) what is the positive difference between the a values for the two functions that describe the parabolas