Everyday Rishab's mom starts from home, drives to his school and reaches there at exactly 4 pm and immediately picks him up from there and drives him back home. One day, Rishab left the school at 3 pm, and without waiting for his mother, started walking towards home. He met his mother on the way and together they reached home 40/3 minutes earlier than usual. If the next day, he left the school at 3:30pm, and started walking towards home, how many minutes earlier than usual did they reach home ???approach please

1) 12
2) 8
3) 20/3
4) 19/3