Question

David leaves the house to go to school. He walks 200 meters west and

Answer 1

Pythagorean Theorem, where a^2+b^2=c^2. Just plugging in the numbers:
200^2 + 125^2=C^2
40,000 + 15,625=C^2
55,625=C^2
Then just take the square root
C=235.8495
If the number needs to be rounded then 236 meters.