You: spends $50 on supplies
charges $10 per hour ⇔
[The number that 10 & 8 both have in
Brother: spends $30 on supplies common is 40]
charges $8 per hour ⇔
↓
You: 10 x 4= 40 [You'll work 4 hours to get the same amount of money.]
↓
Brother: 8 x 5= 40 [Your brother will work 5 hours to get the same amount of money.]