The original planned time is 180/v, and the actual time is 60/v 120/( 1.5v).

Then the formula: originally planned time -40min (that is, 2/3h)= actual time.

180/v-2/3 = 60/v 120/( 1.5v)

The solution is v = 60 km/h.

So the original planned speed is 60 km/h.

Be sure to give strength.