Conditional Rules on Workflow

Hi,

I'm creating a conditional rule for a Workflow. I need it to action if a field has a certain value/values.

I've put the following codes in the Javascript Conditions Box

Valid=(("oppo_priceknown"=='Price Unknown'));

I've gone on to try:

if (values('oppo_deliverypriceknown'=='Price Known'));
valid=true;

else

(values('oppo_deliverypriceknown'=='Price Unknown'));

Valid=false;

Neither of which work.

I've had a previous conditional rule work correctly when the condition is a task being set to 'Complete' or not.

Is it possible to have a conditional rule fire on certain field options?