Any time you are ading or subtracting fractions you want to find like denominators. So first list the multiples of each denominator until you find the smallest number they have in common.
At my school the younger children call it skip counting. 4,8,12
Do the same with the 3=3,6,9,12. So...

Any time your top number, the numerator is smaller than the bottom number your answer is less than one, if top number is equal to bottom the answe is 1. If top number is larger the answer will be greater than 1.

The simpliest way to answer this question is use what you already know. .5 is 50% and .75 is 75% so any fraction that falls between the two would be a correct answer. 6/10, which is 60%, 7/10, which is 70% and 3/5,which is also 60 % but is the reduced fraction for 6/10. Then you can...