Creating index with a string

So I want to create an index for activity level.

We have the following variabeles (I translated a couple of things to english, tis originally in dutch):

v18_1 I am a member of: Sportclub
v18_2 Ik ben lid van een:Music school
v18_3 Ik ben lid van een: Jeugdbeweging
v18_4 Ik ben lid van een: artschool
v18_5_and I am a member of: Other, namely: ….

So I go to computer, then do SUM (all of those variables) . But it doesn't want to create it since the v18_5_and is in letters and not numeric.
How do I create an index out of this?