To determine how far the postman is from his office, we need to break down his walking journey step-by-step, tracking each direction and distance he covers:

1. The postman starts by walking 20 meters straight from his office.
2. He then turns right and walks 10 meters. Assuming he initially headed north from his office, a right turn would mean heading east.
3. After turning left, he walks another 10 meters. From his last position, a left turn from east means he is now facing north.
4. He then turns right and walks 20 meters. A right turn from north indicates he is moving east again.
5. Finally, he turns right and walks 70 meters. A right turn from east means he is facing south.

To find his distance from the office, we should consider his movements in terms of horizontal and vertical displacement:

• Horizontal Movement:
  • He walked 10 meters east (first right turn).
  • He walked 20 meters east (third right turn).
  • Total eastward distance = 10 m + 20 m = 30 m to the east.
  • He walked 70 meters south (final right turn), which means moving back in the reverse horizontal plane, but we only count net distance covered east and west, in this process.
• Vertical Movement:
  • He initially walked 20 meters north.
  • He walked another 10 meters north (turning left).
  • He moved 70 meters south (final right turn).
  • Total net vertical movement = 30 m north (20 m initial + 10 m after first left) - 70 m south = -40 m (40 meters south).

We can now calculate the straight-line distance (D) from the office using the Pythagorean theorem, where the horizontal (x) and vertical (y) displacements are as follows:

D = \sqrt{(30)^2 + (40)^2}

D = \sqrt{900 + 1600}

D = \sqrt{2500}

D = 50 \, \text{m}

The postman is 50 meters away from his office. Therefore, the correct answer is 50 m.