Eric earned 60 points on his last test. if there were 75 possible points, what was his percent grade?

This is a proportion problem. Eric earned 60 out of a possible 75 points, so the ratio is 60/75. You put that equal to x, so 60=x% and 75=100%. So it would look like
60 =   x  
75    100
then you cross multiply 60 and 100, and 75 and x, so you get
6000=75x
then divide by 75 and you have your percent :)

You change a fraction into a percentage by multiplying by 100.

So, for example, half is 1/2. Multiply by 100 gives 100/2=50. So half is 50%.

Here we know that Eric earned 60 points out of a possible 75. So the percentage is:
60 (the points he earned) / 75 (possible score) * 100
= 6000/75 we can simplify by dividing the numerator and denominator by 5 
= 1200/15 and simplify again by dividing both by 5
= 240/3 = 80. So Eric got 80%