Exercise $2(20$ points$)$

$An$ electric power plant uses solid waste for fuel $in$ the production $of$ electricity. The

$costYin$ dollars per hour $to$ produce electricity $isY=12+0\mathrm{.}3x+0\mathrm{.}27x^2,$ where $xisin$

megawatts. Revenue $in$ dollars per hour from the sale $of$ electricity $is15x-0\mathrm{.}2x^2.$ Find

the value $ofx$ that gives maximum profit.