Question

A circle measure 12 feet in diameter what’s its area to the nearest foot

Answer 1

The formulas for the circumference and area of a circle are

$C = 2\pi r,\quad A = \pi r^2$

So, if we isolate the radius from the formula for the circumference we have

$r = \dfrac{C}{2\pi}$

And if we substitute this expression for the radius in the formula for the area, we have

$A = \pi r^2 = \pi \dfrac{C^2}{4\pi^2} = \dfrac{C^2}{4\pi}$

So, if you plug your value you have

$A = \dfrac{144}{4\pi} = 11.4591559\ldots \approx 11$