Given a regression cost function, y = 10 + 2x with a standard error of $3.40, and x represents the activity of direct labor hours, what is the estimated cost when x= 15? a $7.80 c. $40.00 b. $15.60 d. $80.00 Refer to the preceding question. What is the 95% prediction interval, using the non-precise guidelines discussed in the notes, for the true cost when the number of direct labor hours is 15? a. $46.80