A paddock on level ground is 4 km long and 3 km wide. Answer these questions, correct to the nearest second.

a) If a farmer walks from one corner to the opposite corner along the fences in 84 minutes, how long will it take him if he walks across the diagonal?

b) If his assistant jogs along the diagonal in 40 minutes, how long will it take him if he jogs along the fences?

Please help me! Thank you.