Draw the right triangle showing a vertical line for the height "h" of the balloon above the aqueduct's horizontal, the horizontal distance "y" from the base of the vertical to the closer end of the aqueduct, and the slanty line labelled "270" showing the line-of-sight distance. Label the given angle and the right angle.
Solve this triangle.
Extend the horizontal to the other end of the aqueduct; label this additional distance as "x". Draw another slanty line from the balloon to this other end. Label the angle at the balloon.
Using the height "h" that you found from the first triangle and the angle value, find the length of the base "x + y". Subtract "y" to find the length of the aqueduct.