Answer: 445.20 dollars
=============================================================
Explanation:
There are two approaches.
The slightly longer approach will have us take 6% of 420 to get 0.06*420 = 25.20
So 25.20 is the amount of tax you pay on top of the original $420. The total bill is 420+25.20 = 445.20 dollars
--------------
The shortcut is to multiply 420 by 1.06 to get 420*1.06 = 445.20
The 1.06 multiplier indicates an increase of 6%
We can think of it it as 1.06 = 1 + 0.06 = 100% + 6%
