3.80+2.60=6.40$ money that erik need to pay 6.40$ x .05=.32 (.05 represent the 5% coupon) 6.40$ - .32=6.08subtract the percent of the coupon to find the total bill of erik 20$ - 6.08=13.92$ subtract the money that erik needs to the 20$ 13.92$ would be the change that erik receive back