C(x)=4x-2 and d(x)=x^(2)+5, what is (c*d)(x)

Suppose a pendulum is l meters long. the time,t,in seconds that it tales to swing back and forth once is given by t=2.01

In the polynomial below, what number should replace the question mark to produce a difference of squares? x2 + ? x - 36

Could somebody me with this radical simplification?