Tom drove for 3 hours at 30 km/hr and another 2 hrs at 70km/h. What was his average speed for the journey?

attempt:

using S = d/t

Given: 2 hrs at 70km/h and 3 hrs at 30km/h

Solve: 30/3 + 70/2 = (10 + 35 ) /2 = 45/2 = 22.5 km/h

please correct me if im wrong.

because im not so sure with my solution.

thanks