In the good old times, everyone had to go to the tax office and pay taxes. Today, taxes are payed by the employer (so the 95% of Congolese in the informal sector does not pay taxes anymore). Your employer should know, how much taxes are for you.
Following to this link congorama.com/business/pincipimpot you may pay 40–50% taxes on your salary (IPR, table on the bottom) (2000$ = ca. 2 Mio Fc).
2000 $ -> 40% tax free = 800 $
2000 $ -> 60% taxed (45%)
1200 -> 45 % tax = 540 $
1200 -> 55 % sal. = 660 $
TOTAL: 1460 $ salary if 45% taxes
1400 $ salary if 50% taxes