Twin brothers, billy and bobby, can mow their grandparents lawn together in 69 minutes. Billy could mow the lawn by himself in 30 minutes less time that it would take bobby. How long would it take bobby to mow the lawn by himself?
Step-by-step explanation: both brothers can mow the lawn in a total of 69 minutes. Billy can do it in 30 mins so the rest is left for his twin Bobby. 69-30 = 39
