Adam bought a box of fruit that weighed 6 3/8 kilograms. if he bought a second box that weighed 7 2/5 kilograms, what is the combined weight of both boxes?

So you have to get the fractions with the same denominator (the number on the bottom)
the easiest way to do it is just multiply each with the opposing denominator
EXAMPLE: For 3/8 you multiply top and bottom by 5, the other fraction's denominator and you would get 15/40
then for 2/5 you multiply it by 8 and get 16/40
ANSWER: 6 15/40 + 7 16/40 = 13 31/40

The answer maybbe c