Hello, Dunit0001!

Here's #3 . . .

3) Because of traffic Maria could average only 40 km/h for the first 20% of her trip.

But she averaged 75 km/h for the whole trip.

What was her average speed for the last 80% of her trip?

We know that: .

. . and its variations: .

Suppose the trip was 400 km long.

The first 20% is 80 km; the last 80% is 320 km.

She drove 80 km at 40 kph.

. . This took her: . hours.

The she drove 320 km at kph.

. . This took her: . hours.

Then, to drive 400 km, her total time was: . hours.

Hence, her average speed was: . kph.

Since her average speed was 75 kph, we have: .

. . Now solve for