1) To create an equation with r isolated, you divide both sides by π and square root both (it is given that all variables are positive). The equation is √A/π = r.
2) Plugging in the numbers give us √54/(22/7) = r.
√54(22/7) can be rewritten as √54*7/22, which is √378/22, which can be simplified to √189/11, or about 17.18.
