A local television station sells 15-second, 30-second, and 60-second advertising spots. Let x denote the length of a randomly selected commercial appearing on this station, and suppose that the probability distribution of x is given by the following table:
x 15 30 60
p(x) 1 .3 6
a. Find the average length for commercials appearing on this station.
b. If a 15-second spot sells for $500, a 30-second spot for $800, and a 60-second spot for $1000, find the average amount paid for commercials appearing on this station.