Answer:
21
Explanation:
85% is the same as the fraction
, so in order to figure this problem out, you would set that proportional to 3/x. This is going to tell you how many are right.

Now you are going to cross multiply which means you will multiply 85 and x and 3 and 100 so it will look like this:
85x=300
Now you are going to divide by 85 on both sides of the equation to get x by itself. 300/85 = 3.5 and 85x/85 = x which means that x=3.5, but you are not done yet.
The next step is to plug x in so it will look like 3/3.5 since we want to get three wrong we are going to multiply the numerator and denominator by 6 to get 18/21 which is 3 questions wrong.