It is 28 pounds. This is because all of the others have a ratio of 4:1 while 28 and 5.5 have a ratio of 56:13.
Answer:
90
Step-by-step explanation:
To find s4 we find sum of values when n=1,n=2,n=3,n=4
given expression is 
n=1 , plug in 1 for n

n=2

n=3

n=4

Sum of all 4 terms = 6+12+24+48=90
In general, you're calculating the magnitude of average velocity. In fact, speed is a vector, and as such it also has a direction and orientation.
So, if you compute the average speed, you're assuming that you went directly from point A to point B, which is basically never the case.
If, instead, you actually moved on a straight line from point A to point B, then the two quantities are the same.