A body travelling along a straight line path travels first half of the distance with a velocity \(7 \mathrm{~ms}^{-1}\). During the travel time of the second half of the distance, first half time is travelled with a velocity \(14 \mathrm{~ms}^{-1}\) and the
second half time is travelled with a velocity \(21 \mathrm{~ms}^{-1}\). Then the average velocity of the body during the journey is

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.