the correct answers are 4:3 and 16:12. if you divide 8 and 6, you get 1.3 (repeating). you get that same answer for the other two ratios. if you divide the other ones you get different decimals than don't equal 1.3 (repeating) so you can tell they're not correct.
*if i was a little confusing tell me I can explain it better if you'd like*