Circumference = 2 x Pi x R
if we use 3.14 as pi, you would do 2 x 3.14 x 4, which would equal 25.12, i’m not sure if it was meant to be rounded to 25, but none of the multiple choice answers would be correct
See examples before for the method to solving literal equations for a given variable: Solve A = bh for b. Since h is multiplied times b, you must divide both sides by h in order to isolate b. Since (c+d) is divided by 2, you must first multiply both sides of the equation by 2.
Let

. Then

Meanwhile, since

, you have

.
It follows that

,

, and

, so that the quadratic fit for

that satisfies the given points is

Note that this is just the second-order Taylor polynomial for

about

.