ATM PRESSURE- 10 immediate points if you can help me with this question :S? ?

ume the atmospheric pressure y at a height x meters above the sea level satisfies the relation dy/dx = kx. If one day at a certain location the atmospheric pressures are 760 and 675 torr (unit for pressure) at sea level and at 1000 meters above sea level, respectively, find the value of the atmospheric pressure at 600 meters above sea level.