This equation is very difficult for me and i need help with it?

Question

A paper company needs to ship paper to a large printing business. The paper will be shipped in small boxes and large boxes. Each small box of paper weighs 45 pounds and each large box of paper weighs 75 pounds. There were 3 more small boxes shipped than large boxes and the total weight of all boxes was 1455 pounds. Write a system of equations that could be used to determine the number of small boxes shipped and the number of large boxes shipped. Define the variables that you use to write the system.

Answer 1

S = No. small boxes

L = No. large boxes

There are 3 more small than large;

Eqn (1) for the no. of boxes: S = L + 3

Each small box is 45 lbs.; each large box is 75 lbs.

Eqn (2) for the weight: 45S + 75L = 1455

I suggest using substitution method to solve, first for L, then for S.