Hi ustacp,
Hex numbers are simply another form for presenting binary numbers with the values: 0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f representing 0-15 or all the values of binary numbers 4-bits at a time. So, your numbers 7B + 12F can be added as:
0 7 B=0000 0111 1011
1 2 F= 0001 0010 1111
------------------------------
Total=0001 1010 1010=1aa
where:
0000=0
0001=1
0010=2
0011=3
0100=4
0101=5
0100=6
0111=7
1000=8
1001=9
1010=10=a
1011=11=b
1100=12=c
1101=13=d
1110=14=e
1111=15=f
for all 16 values that can be expressed in 4 bits or 2^4th power=16, i.e. the power representing the number of bits.
-- Tom
P.S. Any Linux system should have a calculator application available from the menu pull-down. Just double click it, set the view to scientific notation and select Hex then punch in the numbers and use the arithmetic symbols {+, -, x, ./.} to get the answers. Then there is this website I found by searching for: hex calculator
here.