Solve for x :

Find the relation between x and y if the points A(x, y), B(5, 7) and C( - 4, 5) are collinear.

The 4^th term of an AP is twice its 18^th term. If its 6^th term is - 8, then find the sum of its first 20 terms.

The angle of elevation of an aero plane from a point A on the ground is 60°. After a flight of 15 seconds, the angle of elevation changes to 30°. If the aero plane is flying at a constant height of 1500√3 m, find the speed of plane in km/hr.

If the coordinates of points A and B are ( - 2, - 2) and (2, - 4) respectively, find the coordinates of P such that AP = 3/7 AB, where P lies on the line segments AB.