Vertical X 2 on the left. Scroll down in the Split Screen effects box and note the vertical and horizontal bias and the scale sliders. Use them to move and size (if necessary) the left-side images.
Then load the right-side image. Apply SCALE, CROP, MOTION, POSITION effects, as needed. Use the minimum amount of effects to do the job, and try to avoid duplicating any, such as several Scale effects for one image. How much screen room it takes up on the right side will depend upon its aspect ratio and how you scaled/cropped it.
The tracks containing A, B and the right-side image are stacked on separate tracks, one atop another.
