Question 1096981
h(x)=-x^2+4x+10
average rate of change of a function between a and b
[f(b)-f(a)]/(b-a)
=(-9+12+10)-10 is numerator, and that is 3
=3-0=3 denominator
so average rate of change of the height is 1 foot per hour. 
{{{graph(300,300,-1,5,-10,20,-x^2+4x+10)}}}