How do you write the equation of a line if you know its y-intercept and the equation of a line to which it is perpendicular ?

Andy wants to find the distance d across a river. he located points as shown in the figure, then use similar triangles to find that d = 223.5 feet. how can you tell without calculating that he must be wrong? tell what you think he did wrong and correct his error. round your answer to the nearest tenth if necessary. andy must have used the wrong . the distance d is actually feet.