I was wondering if someone can help me with computation funcationality issue.

What I am trying to do is obtain a $ difference between 2 numbers with
these parameters based upon 3 different levels, 2 different cities, and 3
types of categories.

Computations trying to obtain:
If reference was city 1, cat 1 at L1
Obtain $ difference for that city 1
L1 L2 L3
cat 1 0 Diff $1-$1B $1-$1C
cat 2 $1-$2 $1-$2b $1-2c

The format of the data is:
CITY CATEGORY LEVEL AMOUNT
city 1 cat 1 L1 $1
city 1 cat 1 L2 $1B
city 1 cat 1 L3 $1C
city 1 cat 2 L1 $2
city 1 cat 2 L2 $2b
city 1 cat 2 L3 $2c
city 2 cat 1 L1 $12
city 2 cat 1 L2 $12b
city 2 cat 1 L3 $12c
city 2 cat 2 L1 $22
city 2 cat 2 L2 $22b
city 2 cat 2 L3 $22c

Thanks for your help