Change string parameter length

[technitutors]

Hi All

So I need the value of B to be subtracted by 10. Im not sure what syntax to use. I tried placing B=B-10 in a codex but thats giving me an error

[sovitek]

Hello @technitutors …could you zoom in the image, cant really see whats goin on

[technitutors]

[bvs1982]