Answer:
20 blue, 10 red, 40 yellow. There are no clues to how many black.
Step-by-step explanation:
12)
11-5+x=2x-1
x-2x=-1-11+5
-x=-7
x=7
13)
10+2x+12=x+17
2x-x=17-12-10
x=-5
