Final answer:
The equation of the line in slope-intercept form is y = 3x + 9.
Step-by-step explanation:
The slope-intercept form of a linear equation is y = mx + b, where m is the slope and b is the y-intercept.
In this case, we are given that the slope of the line is 3 and the y-intercept is 9. Therefore, the equation of the line in slope-intercept form is y = 3x + 9.
This means that for every increase of 1 on the horizontal axis (x), there is a rise of 3 on the vertical axis (y), and the line crosses the y-axis at the point (0, 9).