Part A.
C. 8 (a + 2c)
Explanation:
The answer is c because when you have this equation (below) you have find what both numbers are divisible by:

Both of these numbers are divisible by 8 (This number would be on the outside of the parenthesis).

Now that you know they're both divisible by 8 you can start to put together your equation. So far you should have this:
8 (? +?)
Now to find the other numbers you have to think... what number multiplied by 8 will make it equal to 8a? The answer would be a. 8 times a = 8a. (Another way to do this is to just divide 8a by 8 same with 16)
Now your equation should look like this:
8 (a + ?)
Now do the same thing with the 16c as you did with the 8a. (either divide 16c by 8 or think of a number times 8 that will make it equal 16c) For this one I'm going to use the division method - so what is 16c ÷ 8? 16 ÷ 8 = 2 and finally just add the c. So your answer is 2c.
Your equation should not look like this:
8 (a + 2c)
You're done!
Part B.
-56
Eplanation:
To find this just plug in the numbers into the equation. a = -5 and c = -1.
For this I used the original equation :

Plug in the numbers....

And solve!

And finally....

So the value of the equation if a were -5 and c were -1 would be -56!