Answer:By multiplying with (1+0.01x) where x is the percentage of increase, monthly pay rate of 21$ after marked up 78.7% and 10% profit will be $41.28.
Explanation:
Given that pay rate is 21$ and it is marked up by 78.7% and made a 10% profit.
If any value marked up or made a profit of x% then we have to multiply with (1+0.01x) to find the new value.
New pay after 78.7% marked up using above formula is

Now we have to use above formula again for 10% profit.
Hence new value
≈$41.28