Multiplying dimension (feet) by integer

Hello I am trying to multiply a dimension parameter by 3 but it the result from the multiplication node is null. Do I need a node that converts dimension into integer?

thank you in advance.

You are getting null value because the output from the Lunchbox Get Parameter Value node is a string.
Is it necessary to maintain the Feet Inch structure? If not, try using the OOTB node instead?