The bus' speed is 10 mph more than the car's speed: .\(\displaystyle \text{bus} \:=\:\text{car} + 10\) .[1]

The bus drove the same distance in half the car's time.
The bus' speed must be twice the car's speed: .\(\displaystyle \text{bus} \:=\:2\times\text{car}\) .[2]