Passing a calculated value in a hidden_field

I have a calculated number that I wish to use to send as a value in a
hidden_field in a form. This started out as a question, but I figured
it out so I'll post it anyway as a FYI for Ruby Noobs like me or if
anyone can think of a smarter way.

A few points:
*The value is calculated in the controller and assigned to an instance
variable
*The 'TimeOff' model is in a has_many relationship with the 'Employee'
model (An Employee can take many days off).
*The resulting value is being passed as a hidden_field to populate the
table 'time_offs'

Either of these work:

     <%= hidden_field "time_off", "hours_left", :value =>
"#{pto_accrued}" %> <%= hidden_field "time_off",
"hours_left", :value => @pto_accrued %>

Below is my code:

# Employee Model