Answer: standard deviation = 8
This is because mu = 75 is the mean, which is at the very exact center of this distribution. One space to the right is 83, which is 83-75 = 8 units away from the center. This distance is exactly one standard deviation. We can say "83 is one standard deviation larger than 75".
Or you could note the distance from 67 to 75 is also 8, because 75-67 = 8. Each tickmark represents stepping one standard deviation in distance.