A train can travel $75\%$ faster than a car. Both start from point A at the same time and reach point B, $70\text{km}$ away from A, at the same time. On the way, however, the train lost about $18$ minutes while stopping at the stations. The speed of the car is:

Let the speed of the car be $v\text{km/h}$.
The train travels $75\%$ faster than the car, so the speed of the train is:

$$v_{\text{train}}=v\times \left(1+\frac{75}{100}\right)=v\times \frac{175}{100}=1.75v=\frac{7}{4}v\text{km/h}$$

The total distance is $d=70\text{km}$.
The time taken by the car is $\frac{70}{v}$ hours.
The time taken by the train while moving is $\frac{70}{\frac{7}{4}v}=\frac{280}{7v}=\frac{40}{v}$ hours.

The difference between their travel times is due to the $18$ minutes the train stopped at stations. Let's convert $18$ minutes into hours:

$$18\text{minutes}=\frac{18}{60}\text{hours}=\frac{3}{10}\text{hours}$$

Set up the time difference equation:

$$\frac{70}{v}-\frac{40}{v}=\frac{3}{10}$$

$$\frac{30}{v}=\frac{3}{10}$$

$$3v=300$$

$$v=100\text{km/h}$$

The speed of the car is $100\text{km/h}$.