How much money will molly earn if she sells all of the dog beds?

Molly bought 12.5 yards at $4.5 per yard, so she paid

Cost = 12.5 * 4.5 = 56.25

Even though she bought 12.5 yards, she only needs 2.5 yards for one dog bed, well then, how many times does 2.5 go into 12.5?  12.5 ÷ 2.5 = 5, meaning, she can make 5 dog beds from all those 12.5 yards she bought.

She's selling each dog bed for $17.50, so for 5 of those that'll be

Revenue = 5 * 17.5 = 87.5

so now, what's her profit?  Profit = Revenue - Costs, 87.5 - 56.25 = 31.25.