Use the Pythagorean theorem to solve for the diagonal distance
Diagonal = sqrt(50^2 + 150^2)
Diagonal distance = sqrt(25,000)
Diagonal distance = 158.11 feet
Round to 158 feet.
If the stayed on the sidewalk they would walk 50 + 150 = 200 feet.
The distance they saved = 200-158 = 42 feet
Answer: 42 feet.