Whats the proper formula to find the answer to these types of % questions?

[TheGuardner]

? - 8.75%=6818.35

How do I get to the answer?

 

[HallsofIvy]

? - 8.75%=6818.35

How do I get to the answer?

You don't. What you have written makes no sense. You can only subtract a "percent" from another "percent". And then the result would be equal to a percent, not a number like "6818.35". Strictly speaking, you cannot "do arithmetic" with percents: 8.76% is just a way of writing the number .0876. Perhaps you mean (1.000- .0875)X= 6818.36. I presume you know that 1.000- .00875= 0.9125 so this equation is the same as .9125X= 6818.36. Now, to get X alone, divide both sides by .9125.