You don't need maths for this, you need some common sense. No scientist can answer that question without knowing all the variables, on a flat course your weight has little effect especially at 20Km/h, but loosing weight will improve your climbing speed dramatically and almost proportionally with the weight loss, if this was the only change. The climbs are where your average speed would have been dragged down the most. But the process of loosing the 32Kg would increase your fitness level significantly as well, so your speed gain would benefit from this as well.
