Answer:
one large box equals 15.75<em>kg</em>
one small box equals 13.75<em>kg</em>
Step-by-step explanation:
First, identify your variables:
Let "l" represent the weight of one large box.
Let"s" represent the weight of one small box.
Then, stack the two equations on top of each other:

Next, multiply the first equation by 3 so we can use elimination of the "s" variable to find the "l" variable first:

Now, subtract the two equations to cancel out the s-variable and find the l-variable:

Then, substitute your l-variable in the original first equation to find the s-variable:

With all the information that is collected, you find that one large box weighs 15.75<em>kg</em> and one small box weighs 13.75<em>kg</em>.