disabling a tradiobutton

Hi!
I am developing a pascal program using Turbo Vision.
I would like in certain circumstances to disable a TRadiobutton,
the 4th one in a row, where TRadiobutton.Value=3.
The inherited method from TCluster has the EnableMask method which
can be used to disable/enable specific buttons.

Could anybody tell me how to disable the 4th button in a row using
the EnableMask method in the HandleEvent procedure for that Tbutton
variable.

Thanking You,
Kavita