Xiaoming and his father insist on doing morning exercises every morning. Father and son are running on the circular playground. Xiao Gang runs120m per minute, and his father runs180m per minute.

Father and son go to the park for morning exercises in the morning. It takes 30 minutes for the father to run from home to the park, and only 20 minutes for the son. If the father leaves five minutes earlier than the son, it takes 10 minutes for the son to catch up with the father.

The distance from the school to the county seat is 28 kilometers. It needs some distance except by bus. The bus speed is 36km/h, the walking speed is 4km/h, and the whole journey is 1 hour, so the walking time is 1/3 hours.

The downstream speed of a ship is 20km/h and the upstream speed is 16km/h, so the current speed is18km/h.

Xiaoming's current savings deposit in 300 yuan will be withdrawn after three months, with the principal and interest of 30 1.35 yuan (excluding interest tax), so the monthly interest rate of this current savings deposit is 0.45%.