Two cars start at a point A at the same time. The first car goes with a uniform speed of 100 Km/hr and the second car starts at 80 for the first hour and increases the speed by 10 km/hr every hour. After how much time does the second car overtake the first car, assuming these are no stops in between.

Question

$\begin{array}{1 1} 4\;hours \\ 5\;hours \\ 7\;hours \\ 9\;hours \end{array}$