Let 'h' be the height of the tower.
Let D be the point where the angle of depression from the top of the tower is α∘ and C be the point where the angle of depression is β
tan α=1√5,tan β=√5 ...... (given)
In Δ ABC
tan β=hx
√5=hx
x=h√5 …(i)
In Δ ABD
tan α=hy
1√5=hy
y=h√5 …(ii)
To travel (y-x) i.e (h√5−h√5) takes 10 minutes
∴ To travel h√5 will take
10(h√5)h√5−h√5
=10h√55h−h√5
=10h4h=212 minutes