Ok so the total amount the mom paid is 50.50. It says she bought 10 journals at 2.50 each so subtract 25 which leaves 25.50. Then it says 2 markers at 5 each so subtract 10 which leaves 15.50. Then it states she paid 4.10 in annoying sales tax. So subtract 4.10 and you get 11.40 which is the remaining, which means thatbis how much she spent on a mouse.
When you do the inverse operation which in this case would be subtraction you do 54-17 and then you do 17 minus 17 which leaves you with the variable 54-17=34 so k=34
