Answer
Bob's hourly rate is 9 dollars.
Work Step by Step
Let X represent his hourly wage.
Since his hourly rate is X, two times his normal hourly rate means 2 $\times$ X = 2X.
The first 40 hours, he earned his normal wage,so he earned 40 $\times$ X.
For the other 8 hours, because he worked overtime, he earned double his hourly rate, which was 2X. So, for the other 8 hours, he earned 8 $\times$ 2X.
In total, he earned 504.
So: 40 $\times$ X + 8 $\times$ 2X = 504
40X + 16X = 504
56X = 504
Divide both sides by 56
X = 9
