How do you do this? i'm confused on how to start and find my answer.

I'll use 24 as an example.
12.5=0.8x
In order to solve this, you have to get the x by itself. See how the x is being multiplied by 0.8? Well, in order to get rid of the 0.8, you have to the opposite thing: divide 0.8x by 0.8. Since 0.8 / 0.8 is 1, that gets the x by itself. BUT,in order to keep the equation right, you have to do the same thing to both sides of the equation. So, you divide 12.5 by 0.8 too, and you get x=15.625.

If you actually need the answers to all of them ( like for checking ) say so in my inbox.

8x - 61 = 17add 8x = 88x = 11 (cannot be proven)4(3(7) - 8) = 524(21 - 8) = 5284 - 32 = 52 (proven)