First, you would need to determine how much they spent, not including tax.
$7.50 + $5.25 = $12.75
Next, you would need to create an equation for this problem.
($12.75 x 0.15) + $12.75
Now, all you would have to do is solve it.
($12.75 x 0.15) + $12.75 = $14.6625
They spent $14.6625 in total.
I hope this helps!
