Welcome to the forum, hkstudent.
Yes, assuming this is for one person not two, you could apply it to the mixed cabin and it would be 19,500 + 39,000. You can book this online on avios.com
Note however that you may find it better value not to use the voucher for your outbound and instead just for the inbound - it'll cost more avios but will save you a good chunk of YQ. You'd have to call to make that booking though.