L = 0 bcause it cancels itself out
You would have to find the proportionality of the two. If his shadow is 3 feet long, and the tree's shadow is 9 that means it is proportioned by 3. So the height of the tree would be 15.
3n+4=-5
do the opposite of adding 4. this means you have to subtract 4 from 4. whatever you do to the problem, you must do to the answer. now subtract 4 from -5.
-5-4=-9
since 4-4=0, we can take 4 out of the equation. now you have:
3n=-9
now divide -9 by 3
-9/3=-3
n=-3
hope this helps :)