The 40m and 30 m are two sides of a right triangle. The hypotenuese is the distance to the food of the pole. Using Pyhagorian theorem, the hypotenuese is 50 m. That distance and the height of the pole are sides of another right triangle. It’s hypotenuese is the monkey’s displacement from its starting point. Using Pyhagorian again on the 50m and the 120m gives us an answer of 130 m for the displacement.