From the diagram on the right-hand side above,

x\(^2\) = 20\(^2\) - 19\(^2\) = 39 ( from Pythagoras theorem)

x = \(\sqrt{39}\) = 6.245m

As can be seen from the diagram on the right-hand side above,

h = x + 17 = 6.245 + 17 = 23.245 m ≈ 23 m(to the nearest whole number)