I would start by calculating the area of the inner triangle. It's height is 2R (as you note it's 2R from the center to the top vertice, plus 1r from the center to the base), and its base is - do you see why that is? Next find the radius of the larger circle - oh wait, we've already determined that it's 2R - and determine its area. Finally find the height and base of the large triangle so you can determine its area. Then the shaded area is: