Hexadecimal calculations are the same as decimal calculations, which are additions and subtractions of numbers in the same digit, except that hexadecimal is a full 16-digit system. For example: DFH+02H, the calculation process is:

F+2, full 16 carry 1, remainder 1, D+O=D, plus carry 1, becomes E, so the result is E1H. I did not make a mistake. The "H" at the end of course represents hexadecimal and does not participate in the calculation.