Unless I'm missing something, most of the values you are given seem to be irrelevant.
Based on Newton's law of universal gravitation, F=G(m1m2/r^2) where G is the gravitational constant, m1 and m2 are the 2 masses, and r^2 is the distance separating the centres of the 2 masses.
We can substitute the values in to get F=G((1.31x10^22)*(1.55x10^21)/(1.96x10^7)
=3.53x10^18N
Therefore the magnitude of the gravitational force of attraction that Pluto exerts on Charon (and vice versa) is 3.53x10^18N