A solar heater is being designed to heat a pipe that will contain water, as illustrated in

Question:

A solar heater is being designed to heat a pipe that will contain water, as illustrated in the figure. A cross section of the heater is described by the equation x = ky, where k is a constant and all units are in feet. If the pipe is to be placed 18 inches from the vertex of this cross section, find the value of k.