Same, I don't understand with 45K of raw salary how he can only have 5k of tax.

According to: http://www.salaire-brut-en-net.fr/ The after-employer-tax, he should get: 34650k

From which he still need to substract the income tax which is paid directly by employee. It is roughly a month of after tax salary -> 2880.

In total, I would say that a 45k gross income becomes 31k after tax.