Help i really don’t get it and I need it for my test help me please and thank you

Pls , the question is in the picture!

Turner's mom measured his room to see how long the wallpaper border needed to be. if two walls are 15 feet long and two walls are 12 feet long, how long should the strip of border be cut?

Kelly is a salesperson at a shoe store, where she must sell a pre-set number of pairs of shoes each month. at the end of each work day the number of pairs of shoes that she has left to sell that month is given by the equation s=300-15x , where s is the number of pair of shoes kelly still needs to sell and x is the number of days she has worked that month. what is the meaning of the number 300 in this equation