Final answer:
The function for the cost of framing a picture, given a slope of 3 and a y-intercept of 9, is represented by the equation y = 3x + 9.
Step-by-step explanation:
The function relating the cost of framing a picture y to the number of inches of frame x can be represented by a straight line on a graph. According to the given information, this line has a y-intercept of 9 and a slope of 3. The y-intercept is the point where the line intersects the y-axis, and the slope indicates the rise over the run, or how much y increases for a given increase in x.
The equation for a straight line in slope-intercept form is y = mx + b, where m stands for the slope of the line, and b is the y-intercept. Given that the slope (m) is 3 and y-intercept (b) is 9, the equation reflecting the cost of framing a picture concerning the frame size would be y = 3x + 9.