This question seems to be a bit typical, isn't, but it is simplest.
1 red ball can be selected in 4C1 ways
1 white ball can be selected in 3C1 ways
1 blue ball can be selected in 2C1 ways
Total number of ways
= 4C1 × 3C1 × 2C1
= 4 x 3 x 2
= 24
Please note that we have multiplied the combination
results, we use to add when their is OR condition, and we
use to multiply when there is AND condition, In this
question it is AND as
1 red AND 1 White AND 1 Blue, so we multiplied.