Can you guide me through solving this problem: Sally went to the seashore for vacation.  Her parents gave her $10 to buy whatever she wanted.  At the trinket shop, taffy was on sale for "Buy 1 pound at $3, get 1 pound 1/2 off."  She scooped up 2 pounds.  She also bought a mixed bag of seashells for $1.50 and 4 magnets that were $0.25 each.  How much money does Sally have left?