Express the area a of a quake in terms of its perimeter p

Write out the equations for area of a circle and perimeter (circumference) of a circle:

A=pi*r^2                              =pi*r*r

                                                                                               p
C=2pi*r = perimeter = p       = 2*pi*r       so p = 2*pi*r, or r=
                                                                                              2*pi

substitute this last result into the formula for A:
                  p
A = pi [ ]^2            This formula has only one independent variable,                    2*pi                     p.  So, upon simplification of this formula, you'll
                                         end up with a formula for A in terms of p.