Hi Gabby,
You want to find out how much Justin would pay in sales tax. Sales tax is 5% of the purchase, so: $24 x 5% = $24 x 5/100 = 120/100 = $1.20
To find the total amount Justin would pay, add that sales tax amount to the cost of the gift: $1.20 + $24 = $25.20
Remember Justin has $26, so YES he would have enough money to buy the gift