Answer:
[tex]\boxed{25.3 \, \%}[/tex]
Explanation:
1. Calculate the tax
15 % of first $30 000 = 0.15 × 30 000 = $ 4 500
28 % of next $30 000 = 0.28 × 30 000 = 8 400
31 % of next $40 000 = 0.31 × 40 000 = 12 400
Tax = $25 300
2. Calculate the tax percentage
[tex]\text{\% tax} = \dfrac{\text{tax}}{\text{income}} \times 100\, \% = \dfrac{25 300}{100 000}\times 100\, \% = \mathbf{25.3 \, \%}\\\\\text{He pays $\boxed{\mathbf{25.3 \, \%}}$ of his income in federal income tax}}[/tex]