You have that the movie aspect ratio is 2.15 : 1, that is, you have following relation between width and height:
2.15/1 = 2.15 = 215%
that is, the widht is 2.15 times the height, or the width is 215% longer than height.
In order to determine what is the percentage of the image shown, you calculate the percentage that widht is more longer than height. You have a TV of 62.72 width and 35.28 in height:
62.72/35.28 = 1.77 = 177%
that is, width of TV is 1.77 times longer than height, or width is 177% longer.
Hence, on TV will be not possible to watch the complete image. And the percentage shown is of 177%.