Problème de calcul

1. What is the problem? Be very detailed.
bonsoir, je suis entrain de créer un formulaire dans excel j'ai posé plusieurs questions qui demande des chiffres et qui sont facultatives je ne sais pas comment posé la formule de calcul de somme lorsque on aura des reponses à certaine d'entre elle
2. What app or server are you using and on what device and operating system? Include version numbers.
3. What you have you tried to fix the problem?

4. What steps can we take to reproduce the problem?

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.

...several questions that require numbers and which are optional I do not know how the formula for calculating the sum

If you are summing optional values you will have to explicitly convert any null (ie unanswered) ones to 0. See