To find if the first two answers are true, all you need to do is count the number of variables of each type in each equation. This number will be your exponent, since it's the number of times you will multiply that variable by itself.
For your first answer, there are 6 x's. This means that when you multiply the x's together, it will equal x⁶. This is correct.
For your second answer, there are 7 A's and 5 B's. This will equal A⁷B⁵. This is correct.
The last two answers are a bit different. In order to simplify an equation like the ones you've been given, you'd need to put all of your terms in parenthesis in order to say that all of the terms within them must be multiplied by what is outside of the parenthesis. This means that:
(bc)⁶ = (b)⁶(c⁶) = b⁶c⁶, which is correct
xyz⁵ = xyz⁵ ≠ x⁵y⁵z⁵, which is not correct
Your answer will be your fourth option. Hope this helped you out! :-)
