One sign shows 15 miles in 20 minutes what is the speed in miles per hour.

45 miles/hour

Step-by-step explanation:

We need the speed in miles per hour so we need to changes minutes to hours

20 minutes * 1 hour / 60 minutes = 1/3 hour

Speed = distance / time

= 15 miles / (1/3 hour)

=15 * 3 miles/hour

= 45 miles / hour