To find the equation of the line using the ordered pairs (2, 2441) and (5, 2879), we will first calculate the slope (m) using the formula:
\[ m = \frac{y_2 - y_1}{x_2 - x_1} \]
Here, \( (x_1, y_1) = (2, 2441) \) and \( (x_2, y_2) = (5, 2879) \).
Calculating the slope:
\[ m = \frac{2879 - 2441}{5 - 2} = \frac{438}{3} = 146 \]
Next, we use the slope-intercept form of the equation, which is:
\[ y = mx + b \]
Now we can use one of the points to solve for \( b \). We'll use the point (2, 2441):
\[ 2441 = 146(2) + b \] \[ 2441 = 292 + b \] \[ b = 2441 - 292 = 2149 \]
Thus, the equation of the line in slope-intercept form is:
\[ y = 146x + 2149 \]
Next, for part (d), we need to estimate the average annual cost at 2-year colleges in 2015. First, we need to determine the value of \( x \) for the year 2015. If \( x = 2 \) corresponds to the year 2013, then:
\[ x = 2015 - 2013 + 2 = 4 \]
Now we substitute \( x = 4 \) into the equation to find \( y \):
\[ y = 146(4) + 2149 \] \[ y = 584 + 2149 = 2733 \]
So, the average annual cost at 2-year colleges in 2015 is approximately:
\[ \text{The average annual cost at 2-year colleges in 2015 is } $2733. \]