6. A cannon fires a ball upward at 60m/s. How fast will this ball be moving after 4s? A. -60m/s
B. Om/s
C. 40m/s
D. 20.8m/s

i guess that visual aids present persuasive examples to what you are presenting, some factors would be theme (does it fit with the color, information, what you are presenting), size (can you see it, is it a big enough span of data/information), and overall look of the visual aid.

hope this : )

see earlier answer