Objective 3.7

Annual revenue (billions, $) for the Boeing Corporation from 1990 to 2002 is given by
R(t)=.15(t2)2+90\displaystyle {R}{\left({t}\right)}=-{.15}{\left({t}-{2}\right)}^{{2}}+{90}
Annual revenue (billions, $) that Boeing made just from sales of its 737 airplane in the same period is given by
A(t)=0.18(t8)2+30\displaystyle {A}{\left({t}\right)}={0.18}{\left({t}-{8}\right)}^{{2}}+{30}

Note:t=0\displaystyle {t}={0} is January 1, 1990

In what year and month was annual revenue excluding sales of 737s at a maximum?


What was that maximum revenue (in $ billion/year)?
(nearest 0.1 $ billion/year)