What is your current annual income now? Curren annual income is calculated as follows:
Gross income from most recent pay period multiplied times the number of pay periods in 12 months = current annual income. Do that for both jobs, then add them.
For a 4 person household, $40K is not enough for income needed for the I-864 (when applying for Adjustment of Status), imo, since $39K is the I-864p level.