(a) We have three standard 6-sided dice, colored red, yellow, and green. In how many ways can we roll them to get a sum of 9? The dice are colored so that a red 2, yellow 3, and green 4 is a different roll from red 3, yellow 4, and green 2.
(b) We have 10 standard 6-sided dice, all different colors. In how many ways can we roll them to get a sum of 20?
Please explain both of them thoroughly so I can understand!