AJ used linear regression to help him understand his monthly telephone bill. The line of best fit was ˆ y  23.65  1.28x, where x is the number of long-distance calls made during a month, and y is the total telephone cost for a month. In terms of number of long-distance calls and cost:

a. Explain the meaning of the y-intercept, 23.65.

b. Explain the meaning of the slope, 1.28.