A. Not a function since we have the points (-1,0) and (-1,3). The x value repeats while the y values are different. Plugging in x = -1 leads to multiple outputs, which shows we don't have a function. To get a better visual, you can plot the points. You'll see that the points form a vertical line. Therefore, this graph fails the vertical line test.
B. This is a function. All of the x values are different. The points, when graphed, pass the vertical line test. In other words, its impossible to draw a vertical line through any two points on the graph. Any x input here leads to exactly one y output.
C. This is not a function. Like choice A, we have repeated x values. In this case we have (4,6) and (4,7). The x value x = 4 repeats itself leading to multiple outputs y = 6 and y = 7
D. This is also not a function. The x value x = 0 repeats itself. The graph fails the vertical line test.
The answer is actually 31.6 m (3 s.f.). The correct process will be use the sine rule to find out BC and CD. Then find out the length of AC by adding AB (which is 5.8 m) and BC (16.9 m after working out). Then work out the angle of CAD, which will be 46 degrees. Then use the cosine rule on triangle ACD to dine out AD.
