How much did briana save by purchasing a backpack that cost $45 with a sales promotion of 20% off instead of a backpack that cost $42 with a sales promotion of 10% off?

Start by doing a proportion for each one. 20/100 = x/45. 45 times 20 equals 900. 900 divided by 100 equals 9. So 20% off is $9 which makes you pay $36. Do the next proportion. 10/100=x/42. 42 times 10 is 420. 420 divided by 100 equals 4.2. You would get off $4.2 which makes you pay $37.8. $37.8-$36 = $1.8. Your answer is $1.8