Answer: 112 inches.
Step-by-step explanation:
You know that the width of the rectangular piece of wood is 4 inches and the width of the strip ribbon is 1/4 inches.
Then, let be "n" the number of strips ribbon that Laura needs to cover the width of the rectangular piece of wood (Assuming that she will cover the wood in the form shown in the figure attached). This is:

To find the lenght of ribbon that Laura needs to conver the wood, you must multiply the number of strips ribbon "n" by the lenght of the rectangular piece of wood, then you get:

20/2-10/5. You divide 20 by 2 and subtract that from 10 divided by 5
I don't feel like working it out/ maybe someone will give you the answer/ but basically you would set

and add it to

to equal 180( which is the degree of a line
so it looks like this:

and then solve( tell me if you need more clarification)