The transport was traveling at a speed of 70 km / h. It started raining and the driver slowed down to 60 km / h.

The transport was traveling at a speed of 70 km / h. It started raining and the driver slowed down to 60 km / h. When the rain stopped to the destination, it was necessary to drive 40 km. The transport went at a speed of 75 km / h and …

The total distance is equal to the sum of the three distances:
L = u1 * t1 + u2 * t2 + s (km).

The planned arrival time, respectively, is equal to L / u1.
The actual time is T = t1 + t2 + s / u3.
By condition, these times are equal:
(u1 * t1 + u2 * t2 + 40) / u1 = t1 + t2 + s / u3.

We solve the equation:
t1 + t2 * (u2 / u1) + s / u1 = t1 + t2 + s / u3;
After simple transformations, we find that the time it rained was
t2 = (s / u3) * (u3 − u1) / (u1 − u2),
or, substituting numerical values:
t2 = (40/75) * (75-70) / (70-60) = 4/15 (h) = 16 minutes.

ANSWER: it rained for 16 minutes; the average speed is equal to the initial speed u1 = 70 km / h.