frequency distribution

Hi I am stuck at the following example so I could use a little help how to solve it. Question: Find the mean and median of the values of the random variable X, whose relative frequency distribution is given in the table below. X.......Relative Frequency 0.......0.18 1.......0.33 2.......0.10 3.........

I have another question: how do we establish similarity between triangles? Given this figure we're asked to calculate the area of ADG. Given AB=BC=CD and area of CDE is 42. we know that DC: DA is 1:3, but how does he get the same ratio for the bases as well and establish similarity for the 3 triang...