How High Do We Need to Be on Earth to See

Multiple Choice

How high do we need to be on Earth to see 7 miles? On Earth, the distance to the horizon is given by $d \approx \sqrt { \frac { 3 h } { 2 } }$ , where d is in miles to the horizon and h is in feet above sea level.

A) $32 \frac { 2 } { 3 }$ feet
B) $31 \frac { 2 } { 3 }$ feet
C) $34 \frac { 1 } { 4 }$ feet
D) $2 \frac { 2 } { 3 }$ feet
E) $10 \frac { 2 } { 3 }$ feet