Can Someone Help Me With this Heat Flow Problem?

A mountain range can be represented as a periodic topography with a wavelength of 100 km and an amplitude of 1.2 km. Heat flow at the bottom of a valley is measured to be 46 mW/m^2. If the atmospheric gradient is 6.5 K/km, and k = 2.5Wm^-1K^-1, determine what the heat flow would have been without topography; that is, make a topographic correction for the measurement.