let the initial height of the tree be AC
let the point where the tree was broken be B.
the broken part of the tree touches the ground at point D.
given AC = 20mts.
angle of elevation = 30
let the height of the tree after breaking AB = 20 - x
length of the part that is broken = x
in triangle ABD, tan 30 = 20-x/x
1/√3 = 20-x/x
x = 20√3 - √3x
x = 20(1.732) - 1.732x
x+1.732x = 34.64
2.732x = 34.64
x = 12.679 mts
height from the ground which the tree is broken = 20 - x
= 7.320 mts