(1)The percentage error is 6.897 % .

(2)The total cost of the wallet is \$34.35 .

(3)The salesman’s commission as a percent of his total monthly sales is 4% .

(4)The interest is \$5400 .

Step-by-step explanation:

First part

Formula

Change in value = |Approx value – Exact value|

As given

Mark estimates that the distance from his house to his school is 15.5 mi. The actual distance is 14.5 mi.

Approx value =  15.5 mi

Exact value = 14.5 mi

Change in value = |15.5 – 14.5|

= 1

Put all the values in the formula

Percentage error = 6.897 % (Approx)

Thus the percentage error is 6.897 % .

Second part

The price of a wallet is \$31.95 and the sales tax is 7.5%.

7.5% is written in the decimal form

= 0.075

Sales tax price = 0.075 × Price of the wallet

= 0.075 × \$31.95

= \$2.4 (Approx)

Total cost of the wallets = Cost of the wallet + Sales tax price

= \$31.95 + \$2.4

= \$34.35

Therefore the total cost of the wallet is \$34.35.

Third part

Formula

A sneaker store salesman had \$4,125 in total monthly sales last month. He made \$165 in commission from those sales.

Part value = \$165

Total value = \$4125

Put all the values in the formula

Percentage = 4%

Therefore the salesman’s commission as a percent of his total monthly sales is 4% .

Fourth part

Formula

Principle = \$12000

Rate = 15%

Time = 3 years

Put all the values in the formula

Simple interest = \$5400

Therefore the interest is \$5400 .