Final answer:
The equation of a line with a slope of 3 and a y-intercept of 9 is y = 3x + 9, which corresponds to Option A.
Step-by-step explanation:
The equation of a line in slope-intercept form is generally written as y = mx + b, where m represents the slope and b represents the y-intercept. Given the slope (m) of 3 and a y-intercept (b) of 9, we can substitute these values into the slope-intercept form to get the equation of the line. Therefore, the equation is y = 3x + 9.
Looking at the options provided, the correct equation that matches the slope of 3 and the y-intercept of 9 is Option A) y = 3x + 9.