Multiply the cost by the tax, but make sure you make the percentage into decimal form by dividing it by 100.
8.9/100 is 0.089.
0.089x361 is 32.129
Now add the tax due to the original cost.
32.129+361= 393.129
Now round your answer to the hundredths place (cannot have thousandths place when working with money)
$393.13