Respuesta :

first step remove ( )
8a^-7b^3 * -7a^5 b^-9
use exponent rule a^b * a^c =a^b+c
-7 * 8a ^ -2 b^-9 b^3 
-7*8a^-2 b^-6 
-7*8 *1/a^2b-6
multiply fractions 
7*8/a^2b^6
56 / a^2 b^6 
so your answer is 56 over a to the power of 2 b to the power of 6