Answer: 240.3Step-by-step explanation:The 31° angle shown at the top of the figure is congruent to the alternae interior angle inside the triangle at the lower right. "Alternate interior" is language associated with the angles related to a transversal crossing parallel lines. Here, the parallel lines are the horizontal line from which 31° is measured and the horizontal line marked 400 ft. It may not be obvious at first, but the arrow markings on those lines signify that they are parallel. The transversal in this case is the diagonal line marked with an x.So, the length y is opposite the angle you know is 31°, and the length 400 ft is adjacent to it. The mnemonic SOH CAH TOA reminds you that the relation between these is ... Tan = Opposite/AdjacentFilling in the values you know, you have ... tan(31°) = y/(400 ft)Multiplying by 400 ft give ... y = (400 ft)·tan(31°) ≈ 240.3 ft___When you compute this on your calculator, be sure it is in "degrees" mode.