In a bag there are 3 red, 3 yellow, 4 green, and 6 blue marbles. What is the probability of p ( blue ) ?

One really simple way to find an equivalent fraction is just to multiply the numerator and denominator.
For example, for the first answer,
, I simply multiplied the numerator and denominator each by 2. This gives you an equivalent fraction.
You can then continue with this process using numbers such as 3, 4, 5, and 6 as your multiplication factor.