this is just practice problems that I am trying to get a hang of:

a ^-4 b ^3 (a ^7 b ^5)

____________________________

x ^-9 y (x ^9 y ^3)

now the choices I have to choose from are:

a ^3 b ^8

_________

y ^3

a ^3 b ^8

_________

xy ^4

a ^3 b ^8

_________

y ^4

a ^0 b ^10

__________

y ^4

none of these

I need help in learning how to do this type of problem.. Thanks:)