Jawaban:

Let's call the speed of the bus "B". Since the car is travelling at a speed of 90 km/h, we can set up an equation to represent the distance travelled by each vehicle:

Distance travelled by car = 90 km/h x time

Distance travelled by bus = B x time

At 1320 hours, they are 510 km apart, so the total distance they will travel to meet each other is 510 km. We can set up an equation to represent this:

Distance travelled by car + distance travelled by bus = 510 km

Substituting the expressions we derived for the distance travelled by each vehicle, we get:

90 km/h x time + B x time = 510 km

Simplifying this equation, we get:

(90 + B) x time = 510 km

We know that they pass each other at 1620 hours, which means they were travelling towards each other for 3 hours (from 1320 to 1620). Substituting this value for time, we get:

(90 + B) x 3 = 510 km

Simplifying and solving for B, we get:

270 + 3B = 510

3B = 240

B = 80 km/h

Therefore, the speed of the bus is 80 km/h.