You're simply dividing as stated in the picture you provided me, anyways, you're trying to fit "51.419" into "0.376". You should get 51.419 over 0.376 (51.419/0.376), '51.419' will fit 136.752659..., but since it wants you to round it to the nearest thousand, your final answer will be 136.753.
The correct answer is the 2nd choice because -1/6 is closer to 0 and the surface of the pool would be considered 0. -4/6 is farther away from 0 so it is less.