How many ways are there to put five identical red balls and eight identical blue balls into 20 distinct boxes?
A- if at most one ball can be put into each box.
B- if at most one ball of each color can be put into each box?
I don't know if we add up the blue and red. Such as 20C5 and 20C8 and add them up for A but for B I don't know how to start.