Answer
${$200}$
Increase by ${$5}$/hour.
Work Step by Step
Again from part (b), the lawyer earns ${$4000}$/week, so when the government takes tax, it takes all of the lawyer's income at this tax rate.
Divided among 20 workers, each worker will receive $\frac{$4000}{20}$ = ${$200}$, and on an hourly basis, it will increase by $\frac{$200}{40}$ = ${$5}$/hour.