The sales tax is calculated as a percentage of the selling price. In this case, the selling price is $40.00 and the rate of sales tax is 4%.
To calculate the sales tax, we can multiply the selling price by the rate of sales tax:
Sales tax = Selling price x Rate of sales tax
Sales tax = $40.00 x 0.04
Sales tax = $1.60
Therefore, the sales tax for a selling price of $40.00 and a rate of 4% is $1.60. The total cost of the item including sales tax would be $40.00 + $1.60 = $41.60.