1. At this point, the triangle formed by Xiao Ming and the shadow is similar to the triangle formed by the tower and the shadow of the tower.

So the height of the ancient pagoda

= 1.8*(20+2. 1)/2. 1

= 18.9

= 19m

A bamboo pole with a length of 2. 1 m has a vertical shadow length of1.5 m.

The shadow on the wall is actually equal to the length of the flagpole.

So the length of flagpole = 21*11.5+2 =14+2 =16m.