Final answer:
To calculate Iris's total cost including sales tax for two necklaces, add the cost of both necklaces then apply the 8% tax rate to get the sales tax amount. Adding the sales tax to the original total gives the final cost. There may be an error in the provided options as none match the calculated total.
Step-by-step explanation:
To find the total cost of Iris's purchases including sales tax, we first add the cost of both necklaces which are $42.00 and $28.00. The combined cost of the necklaces is $70.00.
Next, we calculate the sales tax by converting 8% to a decimal which is 0.08 and then mulitply it by the total cost of the necklaces:
Sales Tax = Total Cost × Tax Rate
Sales Tax = $70.00 × 0.08
Sales Tax = $5.60
To find the total amount Iris will pay, we add the sales tax to the combined cost of the necklaces:
Total Cost with Tax = Total Cost + Sales Tax
Total Cost with Tax = $70.00 + $5.60
Total Cost with Tax = $75.60
Since none of the provided options matches the correct total, it seems there might be an error in the question or the options provided.