Answer:
7.8 feet
Step-by-step explanation:
The shadow, the ground and the distance between the top of the tree and end of the shadow form 2 right-angled triangles which are similar.
So corresponding sides are in the same ratio. Therefore:-
40 / 12 = 26/x where x is the length of shadow cast by the smaller tree.
40x = 12*26
x = (12*26) / 40
= 7.8 feet