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%.
