Here's a diagram showing how to combine angles LDA (in red) and angle ADE (in blue). Hopefully it becomes a bit clearer why these two angles add up to line segment LE. Erase the shared segment DA if it helps show LE better.
Well your question is a little unclear but say there is a bag of marbles containing 3 green marbles and 6 blue marbles then if you wanted to find the ratio of the green marbles it would be 3/9 or 1/3
