If 2x + 3y = 16 and xy = 9, then find 8x³ + 27y³

In the following figure, O is the centre of the circle. Its two chords AB and CD intersect each other at point P inside the circle. If AB = 18 cm, PB = 6 cm and CP = 4 cm, then find the measure of PD.

If x + y = 25 and xy = 20, then find the value of x³ + y³.

Sohan and Amit started a car race from the same point in the same direction and at the same time on a circular track of length 1125 m with speeds of 36 km/h and 54 km/h, respectively. After how much time (in seconds) will they meet for the first time since the start of the race?