Question

$1,500 computers ; 7% tax

Answer 1

Cost of the computer before tax = $1500
Percentage of sales tax taken = 7%
Then
The amount of sales tax taken = (7/100) * 1500
                                                  = 7 * 15
                                                  = 105 dollars
So the total amount of sales tax taken is $105
Then
The total cost of the computer after adding sales tax = (1500 + 105) dollars
                                                                                     = 1605 dollars
So $1605 is the total cost of the computer after adding 7% tax. I hope the procedure is clear enough for you to understand.

Answer 2

Tax is: 
$1500* (7/100)= $105

$1500+ $105= $1,605

The final answer is $1,605~