Final answer:
To calculate the unit rate, divide the distance by the time, resulting in 7 miles per hour.
Step-by-step explanation:
The student has asked to find the unit rate of speed in miles per hour when given that 21/4 miles are traveled in 3/4 hour. To find the unit rate, we divide the distance by the time.
First, we calculate the rate: (21/4) ÷ (3/4) = (21 ÷ 3) ÷ (4 ÷ 4) = 7 ÷ 1 = 7 miles per hour.
Therefore, the unit rate is 7 miles per hour.