If Irene worked 50 hours last week, the total number of hours counting as overtime is 50-40 = <<50-40=10>>10 hours.
Since she's given $20 for every hour of overtime, she earned 10*$20 = $<<10*20=200>>200 in overtime.
Her total income, including the overtime, is $500+$200= $<<500+200=700>>700
#### 700