90+ 18= 108 (km)

90-18 = 72km

A car: 108÷2=54 (km/h)

Car B: 72÷2=36 (km/h)

A: A's speed is 54 km/h and B's speed is 36 km/h. ..

You can ask if you don't understand. Thank you.

I wish you progress in your study!