21x + 28. just distribute the 7.
Answer:

Step-by-step explanation:
Given
Values: 9/5, 9/5, 2, 9/5
Required
Calculate the sample variance
Sample variance is calculated using:

First, we calculate the mean




becomes





<em>Hence, the variance is 0.01</em>
Let's treat the speed in one hour as a variable.
We can say that 1500=12.5x
Divide by 12.5
1500/12.5 = x
x = 120
120 mph is your answer.