Simple way to answer the following step by step?

Let's assume that all candies in Lisa's bag are either blue, green or red.
Well, then we have two relational pieces of data :

1/4 of the candies are blue.
1/8 of the candies are red.
The common denominator is 8, so :

2/8 are blue
1/8 are red.
This sums up to 3/8 of the total.
The rest of 5/8 of the candies correspond to a third piece of information, a given number :

10 candies are green. So :

5/8 ~= 10 | (/ 5),
1/8 ~= 2

Hence, there are 2 red candies (1/8), 4 blue candies (2/8 = 1/4), and the 10 green ones.
All in all, there are 16 candies in Lisa's bag.