When do we add exponents and when so we multiply exponents?
If we have a variable raised to a power times another variable raised to a power, we add the exponents.
For example, x^2 * x^5 = x^7
If we have a variable raised to a power and that quantity is raised to another power, then we multiply exponents.
For example, (x^2)^5 = x^10
It's easy to illustrate this.
x^2 * x^5
Think of x^2 as x * x and x^5 as x * x * x * x * x
Notice there are 7 x's total, therefore when multiplying it's x^7.
Think of x^2 * x^2 * x^2 * x^2 * x^2
and x^2 = x * x
Therefore we now have x * x * x * x * x * x * x * x * x * x = x^10