§ 3. Rate of tax. -- The tax imposed by section two shall be determined in accordance with the following table: If the city taxable income is: The tax is: Not over $1,000 0.4 % of the city taxable income Over $ 1,000 but not over $ 4 plus 0.6 % of excess over $ 3,000 $1,000 Over $ 3,000 but not over $ 16 plus 0.8 % of excess over $ 6,000 $3,000 Over $ 6,000 but not over $ 40 plus 1.0 % of excess over $10,000 $6,000 Over $10,000 but not over $ 80 plus 1.2 % of excess over $15,000 $10,000 Over $15,000 but not over $140 plus 1.4 % of excess over $20,000 $15,000 Over $20,000 but not over $210 plus 1.6 % of excess over $25,000 $20,000 Over $25,000 but not over $290 plus 1.8 % of excess over $30,000 $25,000 Over $30,000 $380 plus 2.0 % of excess over $30,000