starting out freelancing!! whats the going rate i charge to brands wanting to buy my designs to put on tee's???? cheers!

Hi guys!

Excuse the blunt and quick message but i gotta go change my boys nappy!!!
Might have some designs requested by a tee shirt/clothing label, its for them to put onto tee's, whats the 'going-rate' i should charge per design??
Any feedback is welcome!

Matt:bye