Help with solve block - errors

[pzimpelman]

I already defined the solve block variables but mathcad is still giving me an error that shows that the variable/equations are undefined. 

Can anyone help me find the error here so I can find variable P?

Thanks!

[RichardJ]

You first need to fix a units problem. Mathcad insists P has units of force, in which case sigma(P) has units of pressure. It therefore cannot be equated to sigma[n, which has units of force.

[LucMeekes]

As Richard said, it's a units problem.

Your solution would be:

But when evaluated:

Success!
Luc