the tree is going be perpendicular to the ground so there is the 90 degree angle. The line on the ground from the base of the tree to the broken branch is 10m and because the branch broke you will subtract 10 from 19 to get 9 for the remainder of the tree.
so it will be set up...

Best way from experience: JUST START WRITING. your thesis should be the last thing you write. Once you have completed your conclusion, bounce it back to become the intro and you will find your conclusion summarizes your main points and ties them all together
which is what...

1. first solve for one of the variables in one of the equations
9x+10y=21 ---> 9x=21-10y ---> x=21/9 - 10y/9
2. plug your newly modified equation into the second equation for x
7(21/9 - 10y/9) + 11y=26
3. now you can begin to solve for y
-first distribute...