Hello, Joanna,
The question may be misphrased. I'll interpret "write an algebraic equation to represent the given the information of a rectangle." to
"write an algebraic equation to represent the area of a rectangle."
If this is correct, then the following should help.
Area of a rectangle is L*W = Area
We know that L = W + 5cm
Then the area may be written as Area = (W+5cm)*W
Area = W2 + 5W