Here's what i did:
I broke down the fraction entirely.
3 / 5 = 6 / 10
divide 6 by two and divide 18 by two. This makes 3 / 10 = 9.
divide 3 by three and 9 by three, making 1 / 10 = 3.
if you need 7 / 10 of the number (30) then do 3*7.
The answer is 21.
So we know that an average is the sum of the scores divided by the number of scores that were added together. In this case we are going to be dealing with 4 tests. So let's say x is the score for our fourth test. We can create this equation:

So then we need to simplify the top:

Then multiply by 4 on both sides to get rid of the denominator:

Then solve for x:

So now we know that Sam needs to score a 67 on the fourth test to have an average score of 50.
Ok so you have 4, x^6 / 2, x^4. Now divide the coefficient so 4/2=2. So 2 x^6/x^4, now subtract the numerator by the denominator so x^6-x^4=x^2 so now you have 2x^2
Answer: 2x^2