How to find difference between two columns data?

How to find difference between two columns data?

I have a temp table with two columns of integer data i want to find the
difference between two columns in 3rd column.
#TEMP1
Present previous
59 88
75 75
45 45
77 88
09 08
#temp2
Difference
29
0
0
11
-1
Is this possible ??