(-3m^{2}n^{3})^{2 }(-2m^{3}n)^{ 3}(1/72m^{2}n^{3})

Use PP -3m^{2}n^{3 }must be multiplied 2 times and -2m^{3}n must be multiplied 3 times, but 1/72m^{2}n^{3 }does need to (Because there is no exponent, and that is same as that there is 1).

(9m^{4}n^{6}) (-8m^{9}n^{3})(1/72m^{2}n^{3})

It can be multiplied with same bases.

-72m^{13}n^{9}/72m^{2}n^{3}

And it can be divided

-m^{13-2}n^{9-3}= -m^{11}n^{6}

We can get the results that a is -1, b is 11, and c is 6, so -1+11+6 is equal to 16