To solve this, you must think of the monument and its shadow and Adam and his shadow as a triangle, the person/object being the vertical leg, the shadows being the horizontal leg, and a line connecting them being the hypotenuse. Also, we can assume that these triangles are similar. First, we can set the scale to be 40/5 (the two shadows set a scale because the triangles are similar). Then, we can put x/6 (the actual things are similar, and the scale was established to be building/measurement). Next, we can set the two fractions equal to each other (40/5 = x/6) and solve. We can cross multiply to get 5x = 40 * 6. That goes to 5x = 240. Finally, we can divide by five on each side to get x = 48 feet (D).
