20. A backpack that normally sells for $39 is on sale for 33% off. Find the amount of the discount and the sale price.
21. In August, the Simons' water bill was $48. In September, it was 15%
lower. What was the Simons' water bill in September?
22. A gallery owner purchased a very old painting for $3,000. The painting
sells at a 325% increase in price. What is the retail price of the
painting?

$26.13 sale price. $12.87 discount amount

Step-by-step explanation:

Discount is $39 * 33% (.33)= $12.87

Sale price is $39-$12.87=$26.13

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.

part a: 1.08

part b: 27.59