Let's assume that the average cost of a math textbook in 1990 was $50 and that the cost has been increasing at a rate of $4 per year since then.
To find the equation in the form y = mx + b, we need to determine the slope (m) and the y-intercept (b).
Slope (m): The rate of increase in cost per year.
In this case, the rate of increase is $4 per year, so m = 4.
Y-intercept (b): The initial cost in 1990.
In this case, the initial cost is $50, so b = 50.
Therefore, the equation is:
y = 4x + 50
To predict the average cost in 2016 (x = 26 since it's 26 years after 1990), we substitute x = 26 into the equation:
y = 4 * 26 + 50
y = 104 + 50
y = 154
Therefore, the predicted average cost of a math textbook in 2016 is $154.