If you have an iPhone which I do you can use it’s provided calculator ...I added 11.00 and 5.56 together and I ended up with 16.56 and there’s a % button on it and it does calculations for you.. so I added 7% to the order and it spit out $1.59 then I pressed add and it gave me $17.71 subtract 20.00-17.71 you get $2.29 which is your answer
