For the sake of simplicity, let's assume curators get no part of the payout (which isn't the case). Half of your payout will be payed as SBD. So for a $40 post, you'll get 20 SBD and $20 worth of Steem Power. The value of SBD fluctuates a lot, but right now, 1 SBD is worth $2.54.

That means you'll earn $50.80 worth of SBD (20 SBD) and $20 worth of Steem Power, for a total of $70.80.