The function c(w)=0.013w^2-w-7 estimates the wind chill temperature c(w) at 0f for wind speeds w from 5 to 30 miles per house estimate the wind chill temperature at 0f if the wind speed is 20 miles per hour

For this case, the first thing we should use is the following equation:
 c (w) = 0.013w ^ 2-w-7
 We note that w = 20 belongs to the interval [5, 30]. Therefore, we can use the equation.
 Substituting w = 20 we have:
 c (20) = 0.013 * (20) ^ 2- (20) -7
 c (20) = - 21.8
 
 the wind chill temperature at 0f if the wind speed is 20 miles per hour is:
 c (20) = - 21.8