In order to solve this, we first need to convert the percentage into a decimal. We can do this by either multiplying the percentage by 100, or (my personal shortcut) just moving the decimal point over two places to the left.
4% = 0.04
Now, we need to multiply the decimal by the amount of money we have.
450 * 0.04 = 18
Now, we need to add this newfound amount to the total, since we are adding the 4%
450 + 18 = 468
$450 + 4% = $468
Hope that helped =)