Due to tommarow i will mark as brainliest

30 feet



Work Shown:

x = height of tree in feet

The larger triangle, and the smaller triangle that fits inside the larger, are similr triangles.

So we can form the proportion 
x/5 = 48/8
Note how x/5 is the result of dividing the larger vertical side (x) over the smaller vertical side (5)
The same applies with 48/8. The larger triangle's horizontal side is 8+40 = 48. The corresponding horizontal side for the smaller triangle is 8

Cross multiply to solve for x
x/5 = 48/8
8*x = 5*48
8*x = 240
8*x/8 = 240/8
x = 30

The tree is 30 feet tall

Element 17 is chlorine it is a group 7 element(halogen) and belongs to period 3 of the periodic table