A function is a relation where each input has its own output ( each x values has its own corresponding y value ) If an input has more than one output than the relation is not a function.
We can tell if a graph shows a function or not by using the vertical line test. If you draw vertical lines on the graph and more than one point is on the vertical line drawn then the graph does not show a function.
For graph B if you draw a vertical line at x = -2 more than 1 point will be on the line meaning that the graph does not show a function.
For Graph C if you draw a vertical line at x = 2 more than 1 point will be on the line meaning that Graph C also does not show a function.
For Graphs A and D you can draw a vertical line anywhere on the graph and no more than 1 point will be on the line therefore Graphs A and D show functions.
Relations are only functions if they do not share any x values at all! The 2 graphs there that do not have any of the same x values are graphs A and D. Notice that on graph B, there are several y values that share the x value of 2; on graph C, there are several y values that share the x value of 2.
The area of the scale drawing would be 1080 square centimeters or (1080 cm^2). I got this answer through first finding the area of the classroom in feet (which is A= lw = [18][20] = 360 ft^2) and then I proceeded to converting it to centimeters via given scale factor (3 cm = 1 foot) and had the answer of 1080 centimeters squared.