We first convert the time of 4 hours 20 minutes in minutes 2 hours 20 minutes = 2 × 60 + 20 = 140 minutes

Average speed S is given by distance / time.

Hence S = 280 miles / 140 minutes = <<280/140=2>>2 mile / minute

There are 60 minutes in an hour so the speed is 2*60=120 miles/hour

# Answer

120
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Emma traveled by car 280 miles in 2 hours 20 minutes. What was the average speed of the car in miles per hour?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
120
Emma traveled by car 280 miles in 2 hours 20 minutes. What was the average speed of the car in miles per hour?
train