Answer :
Basically we need to find the slope:
[tex]\begin{gathered} avg=\frac{f(b)-f(a)}{b-a} \\ \text{Where:} \\ a=0 \\ b=7.2 \\ f(a)=420 \\ f(b)=0 \\ avg=\frac{0-420}{7.2-0}=\frac{-420}{7.2}=-\frac{175}{3}\approx-58.33 \end{gathered}[/tex]Basically we need to find the slope:
[tex]\begin{gathered} avg=\frac{f(b)-f(a)}{b-a} \\ \text{Where:} \\ a=0 \\ b=7.2 \\ f(a)=420 \\ f(b)=0 \\ avg=\frac{0-420}{7.2-0}=\frac{-420}{7.2}=-\frac{175}{3}\approx-58.33 \end{gathered}[/tex]