A converging lens forms an image at 40 cm. A 9 cm tall object is placed in front of the lens at a distance of 78 cm. Determine the focal length of the lens.

The number of passengers who arrive at the platform of a subway station for the 10 am train is a random variable with a mean of 120 and a variance of 16. find the lower bound of the probability that there will be between 100 and 140 passengers (round off to second decimal place).