How do I find linear speed of a speed of earth?

All objects on the earth's surface are rotating with the earth. Are all points on the earth's surface moving at the same linear speed as a result of this rotation? To do this problem, compare how far a point on the equator travels during one rotation to how far a point at a higher latitude travels during one rotation (use 40 degrees North latitude as that higher latitude). Then compute the linear speed at which the points are moving. Express the answers in km/hr. ume that the earth is a perfect sphere with a radius 6378 km.