We know the rate of change of h(x) is given by the coefficient of x, -5/7. This means any change in x will be reflected as a change in h(x) by -5/7 times the amount of the change.
Here, we're talking about a change in x of -21, so the change in h(x) will be ...
(-5/7)·(-21) = 5·(21/7) = 15
The positive sign means the value of h(x) will increase by 15.
