So you basically, just make it a ratio. Since a percentage is out of 100, just make the 5 into 100. To get 5 to 100, you times 20. Then you do the same thing to the 4 which you get 80.
Finding the lengths of the legs of the right triangle, we have 6 and 3. (6*3)/2 = 9. Finding the area of the semi-circle we obtain which rounding to 3.14 as pi, we obtain 3.5325. Adding up the area of the triangle and the semi-circle and the triangle we get 9+3.5325 which equals 12.5325