PLEASE HELP ME WITH THIS

What is the value of x when x + 7 = 21?

Use composition to determine if (x) or h(x) is the inverse of f(x) for the limited domain x2-1.

Astudent draws two parabolas on graph paper. both parabolas cross the x-axis at (–4, 0) and (6, 0). the y-intercept of the first parabola 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? write your answer as a decimal rounded to the nearest tenth