Semi-OT: Hourly rate and rake, check my calculations?

[texnewb]

Hi, just wanted to check if I'm doing this right. Doesn't seem correct, at least, I hope I've stuffed up here somewhere.

Estimates from rakeback.com:
$3/$6 FR LHE, 4-tables, 20 hours/week, 25% rakeback
Weekly rake $640 and rakeback $160

So hourly wage for 2BB/100 winrate with 260 hands/hr
= (2 * $6BB) * 2.6 lots of 100 hands/hr = $31.20/hr
for a 20 hour week
$31.20/hr * 20 hours = $624

After rake and rakeback
$624 - ($640 rake - $160 rakeback) = $144 total profit for the 20 hour week (or, $7.20 an hour)

Tell me I'm screwing up here somewhere.
PS: Apologies if posted in wrong forum