Hello!
to find a percent, convert the percent to a decimal by dividing by 100
13.8 / 100 = 0.138
then multiply the divided percent by the number you needed to find the percentage of
$29.90 * 0.138 = $4.1262
since you're using currency, round the the nearest hundredth
your final answer is $4.13
I hope this helps, and have a nice day!