Help please.

Advice on how to add a row of cells (e.g. a1 - a5) as a
corporate sum (shown in A6) where each cell is shown in
the cell by a letter of the alphabet representing a sum
figure.

i.e

A + B + C + D + E = 15

(where a=5; b=4; c=3; d=2 and e=1)

Thanking you.