Answer: \(p^0q^{-5}r^{-\frac23}\), so \(a=0\), \(b=-5\), \(c=-\frac23\).

First simplify the numerator:

The denominator is

\((p^2r)^{-1}q^3=p^{-2}r^{-1}q^3.\)

Dividing by this is the same as multiplying by its reciprocal:

\(p^{-2}q^{-2}r^{-\frac53}\cdot p^2r q^{-3}.\)

Combine the powers of each letter:

Therefore

\(a=0,\qquad b=-5,\qquad c=-\frac23.\)