Question

$20 and $13 both with a 7% sales tax show work

Answer 1

$20x.07= 1.40
$13x.07=0.91

Answer 2

20 + 13 = 33
33 x .07 = $2.31
That's the sale tax.

33 + 2.31 = $35.31

Not sure exactly what you wanted, but I gave both possible answers.
-104 (Commo Doggo)