if i select hiring from department billing type will be editable.Otherwise it set to none and read only.How handle this?
Please set the eval condition in “Read Only Depends On”. Kindly provide more details about your use case so we can better understand what you mean.
When the department is hiring, I have to select a billing type from any of the options. For other departments, I do not need to select a billing type; it will be set to ‘none’ from the options.
but where is the billing type in image ? 
If billing type is a custom field then set the eval condition on that field like
eval:doc.department=="hiring"
eval:parent.department=="hiring"