Question 7
A train travels from $A$ to $B$ at a constant planned speed. After 70 km, the driver notices an engine fault and proposes reducing the speed by 25%. The captain calculates that this would cause a delay of 1 hour 20 minutes. Instead, he asks the driver to continue at the original speed for another 40 km before making that reduction. The train then reaches $B$ exactly 1 hour late. Find its planned speed, in km/h.