There are two ways to calculate his new pay. Choose whichever is easier for you.
OPTION 1:
multiply current pay by 20%, then add the result to the current pay
Step 1:
multiply pay by 20% increase
=$455 * 20%
=$91 increase
Step 2:
add pay increase from step 1 to current pay rate
=$455 + $91
=$546 new weekly rate
OPTION 2:
multiply current pay by (1 + 20%)
=($455)(1 + 20%)
=(455)(1.20)
=$546 new weekly rate
ANSWER: His new weekly rate is $546 per week.
Hope this helps! :)