How do you do this and what's the answer? pls explain.

You don't really need to do any calculations for this as the picture gives it away, but let's just understand the important concept behind this. Basically, tangent is opposite divided adjacent. So for this question:

When you solve for x, you are left with:

Then you need to add the 5 because his eyes cover up the bottom part of the tree, and therefore, your answer is D.

i think it would be 42cm