The monthly average high temperatures in degrees Fahrenheit at Daytona Beach can be modeled by
$$ P(x)=0.0145 x^{4}-0.426 x^{3}+3.53 x^{2}-6.23 x+72 $$
where $x=1$ corresponds to January and $x=12$ represents December.
(a) Find the average high temperature during March and July.
(b) Estimate graphically and numerically the months when the average high temperature is about $80^{\circ} \mathrm{F}$.