You have to deal with a couple of issues: these are not "numbers" according to Excel (double negative signs to coerce the result to be a number), and the sum has to take into account those situations in which the number to the right of "c" is absent (the condition in the IF formula).
I assume that the letter will always be "c" in the string. If so, then in A2, put this formula:
=IF(LEN(A1)-LEN(LEFT(A1,FIND("c",A1)))=0,0,--(RIGHT(A1,LEN(A1)-LEN(LEFT(A1,FIND("c",A1))))))
Then copy it to the right so that B2:F2 are filled with the corresponding formulas.
Then in G2 put
=SUM(A2:F2)