Not much of an explaination needed.
(9/4 + 9/8)/9/2=
You could multiply all child fractions with the same number, to remove them.
In this case, 8 would be the best choice to get rid of them. This works as we add the same value both above and under the fraction.
(8*9/4 + 8*9/8)/8*9/2=
(18+9)/36=27/36=3/4
The answer is 3/4 :)