Interfacing of CO2 sensor module with Arduino ATMega328 through ttl

dear friend,
i m able to receive the data as per need. now i need to formulate. on serial port, i m getting 5 values for example A B C D E and i wanna use in formula 4 and 5.
the formula for this as following:
((128*D+ E)-1000)/100
I would really appreciate you guys. if u can give some solution.

thanks