If he made $300,000 his federal taxes are estimated at $80,904.
This is 26.97% of his estimated total income of $300,000.
If he made $400,000 his federal taxes are estimated at $115,612.
This is 28.9% of his total income of $400,000.
The above is computed with 0 deductions and I could be wrong due to lack of information.
State taxes are not included.