Two cars A and B are moving in the same direction along a straight line with speeds 100 km / h and 80 km / h, respectively such that car A is moving…

Two cars $\displaystyle A$ and $\displaystyle B$ are moving in the same direction along a straight line with speeds $\displaystyle 100 \mathrm{~km} / \mathrm{h}$ and $\displaystyle 80 \mathrm{~km} / \mathrm{h}$, respectively such that car $\displaystyle A$ is moving ahead of $\displaystyle \operatorname{car} B$. A person in car $\displaystyle B$ throws a stone with a speed $\displaystyle v$ so that it hits the car $\displaystyle A$ with a speed of $\displaystyle 5 \mathrm{~m} / \mathrm{s}$. The value of $\displaystyle v$ is $\displaystyle \_\_\_\_$ km/h.