We can make a system of equations with the information given:
Let x be the weight of each large box
Let y be the weight of each small box
Then,
(1) 6x+5y=115
(2) 2x+3y=47
Now, we are going to isolate one variable on one of the equations, and then substite on the other:
(2) 2x=47-3y
x=47/2-3/2y
Now, we are going to substitute (2) in (1)
Then, having the weight of each small box, we are going to substitute y=6.5 in (2)
Each large box weighs 13.75 kg and each small box weighs 6.5 kg.