The probability of taking an orange marbe out, equals the amount of orange marbles divided by the total amount of marbles.
Since there are 3 yellow, 6 black, 3 green and 9 orange marbles, the total number of marbles is:
[tex]3+6+3+9=21[/tex]The probability of taking an orange marble out, will be:
[tex]\frac{9}{21}=\frac{3}{7}[/tex]Therefore, there is a 3/7 probability of taking an orange marbe out.