Question 66709
Think about similar triangles in which corresponding sides are proportional.
In one of the triangles, you have the height which represents the height of the tree and the base which represents the length of the tree's shadow.
In the other triangle, you have the height which represents the metre stick and the base which represents the length of the stick's shadow.
So, based on the above, we can write and solve a proportion in which h = the height of the tree.  It goes like this:
The height of the tree : the height of the metre stick as the length of the tree's shadow is to the length of the metre stick's shadow.
In algebrese, this looks like:
{{{h/1 = 10/0.4}}} 
{{{h = 25}}}...and since the given dimensions were in metres, the answer is:
h = 25 metres.