Boubacar went to the store to buy some walnuts. The price per pound of the walnuts
is $6.50 per pound and he has a coupon for $3.75 off the final amount. With the
coupon, how much would Boubacar have to pay to buy 4 pounds of walnuts? Also,
write an expression for the cost to buy p pounds of walnuts, assuming at least one pound is purchased.