Answer:
? = -2
Step-by-step explanation:
The division law of exponents states that when two numbers with the same base are divided, the exponents will subtract:

This means that the answer is:

Now we just need to convert the answer into the form the question needs.
The power of a power exponent law states that when an exponent is raised to an exponent, the exponent are multiplied, so:

This also means that 
Since our <em>ab </em>is -10, we just need to divide it by the <em>a</em>, which is 5, to get our <em>b</em>, which is the ?
-10/5=-2
Therefore the ? = -2
Hope this helped!