Trouble with Solve Block - Undefined variable?

[aprice]

Hello,I am having trouble using the solve block, specifically the find function. I am completely new to this, and have tried researching on and double checking variables, but I cannot seem to find the problem. I have attached the file.

Thanks for any ideas

EDIT: I am running Mathcad 15 trial on W8.1

[Werner_E · Accepted solution]

You have neither defined a value for the variables b.2xi2 and b.4eta4 not do you solve for them. So the error message is correct in your case.

The "This variable is undefined" error is the only error you will get from a solve block - no matter what the real reason is. Right click on the faulty expression and chose "Trace Error" to get (sometimes) a more meaningful error message.