sketch variables

Hi there, i cant seem to get my variable to work in this sketch. can anyone help? *i have just saved the file with a numeric value https://cad.onshape.com/documents/dfd463c329baadcb71cf923a/w/7641a894ea47965649c0d62c/e/a4d1fb8632ab60571edbb2a6 note i have no problems with using variables in the top plane - see the last…