the calculation of hexadecimal is the same as that of decimal, which is the addition and subtraction of numbers with the same digits, except that hexadecimal is full of hexadecimal digits. for example: dfh+02h, the calculation process is:

f+2, carrying 1 when full, leaving 1, d+o=d, adding carry 1, becomes e, so the result is e1h. that's right. the "h" at the end of course represents hexadecimal and does not participate in calculations.