He paid for 4 pounds of bananas with a 10$ bill. However, they gave him $4 back, so that's mean the total cost for 4 pounds of bananas was for 6 dollars. Now they ask you to find the cost for 1 pound of banana.
4 pounds ............> $6 1 pound.............x (x represents the cost that we are looking for) Cross multiply 4x = 6 Divide both sides by 4 4x/4 = 6/4 x = 1.5 The final answer is : The cost for 1 pound of banana was for $1.5 dollars.