Each of the first 4 pit stops a race car driver makes loses ten seconds off the leader. the pit crew makes adjustments, and at each of the next two pit stops he gains 7 seconds on the leader. how much time is the driver off the leader? show work
a. -40 seconds
b. 14 seconds
c.-26 seconds
d. -54 seconds

First off we start by the four first pit stops. 
Begin at 0 seconds, then subtract 10 seconds from 0 seconds every pit stop. 

Stop 1: 0-10= -10 seconds
Stop 2: -10-10= -20 seconds 
Stop 3: -20-10=-30 seconds
Stop 4: -30-10= -40 seconds

Now we are -40 seconds from the leader. Since the pit crew has made adjustments for the next two stops, we add 7 seconds. 

Stop 5: -40+7= -33 seconds 
Stop 6: -33+7= -26 Seconds from leader. 

The answer is C) -26 seconds 

If the diameter is 8 than the radius is 4 because 2r or 2*radius equals the diameter. 4*2=8. 8/2=4.