The most accurate way is to look at what she earns in a year, because we know there are 52 weeks in a year and there are 12 months in a year. Apart from February, the months do not have exactly 4 weeks in them, so if we used 1 month=4 weeks we would get an inaccurate answer.

36 hours a week is 52×36=1872 hours per year at $21.22 per hour earns $39723.84 a year.

In one year she receives 12×2=24 pay checks because she is paid twice a month. Her deductions are about 24×382=$9168 per year. That leaves her with $30555.84 net per year, so that’s 30555.84/12=$2546.32 per month.

Now let’s compare this using 1 month=4 weeks. That’s 4×36=144 hours a month at $21.22/hr=$3055.68. Her deductions in a month are 2×382=$764, leaving her with $2291.68 net. This is significantly lower than the calculation earlier. The difference is that a 4-week month gives us 48 weeks in the year=1728 hours instead of 1872, and the total pay is $36668.16 instead of $39723.84. That’s a difference of $3055.68 a year or $254.64 a month! This is the difference between the net pay amounts because the deductions are the same (she could buy some nice clothes with this difference!).