I'm going into a little friendly weight loss competition with a female co-worker. I know bf% would be helpful, but I was wondering what would be fair for amount of weight loss for each of us.

I'm a 28 year old male, 6'1" tall, and weigh 215 lbs.
My competition is a 55 year old female, about 5'9", and about 240 lbs.

Should we just make it equal and go with # of pounds or set a % loss to be fair?