If you had 4 boxes of cereal and each costs $2.40, the total cost would be $9.60 (2.40×4).
The total cost of the bananas and the cereal cost $10.11. To find how much the 3/4 of bananas cost, simply subtract $9.60 away from $10.11 (10.11-9.6), which gives you $0.51.
The question asks for 1 pound of bananas but you only have the cost of 3/4. So, divide your cost by 3 to give you the cost of 1/4. (0.51÷3), which gives you $0.17.
The last step is to multiply this answer by 4 because 4/4 will result in a whole, or in this case, one pound (0.17×4) and thus gives you the cost $0.68 for one pound of bananas.
(please correct me if I'm wrong, hope this helped c: )