To find his net income, the first step is to substract the taxes from the salary, this way:
[tex]\begin{gathered} 4500-0.062\cdot4500-0.0145\cdot4500-0.15\cdot4500-0.0765\cdot4500= \\ 4500-0.303\cdot4500=3136.5 \end{gathered}[/tex]Now, substract his health insurance to the salary after taxes are deducted.
[tex]3136.5-120=3016.5[/tex]It means, his monthly net income is $3016.5.