What is the equation x=y+z solved for z

X=y+z
subtract y from both sides
-y+x=z that is your answer

Based from the jar you have 4 R's for red
7 B's for blue, 5 G's for green therefore caculations add up to 16 marbles in total. a. chances of finding a red marble gives you 4 over 16 (4/16) or reduce that and get 1 over 4 (1/4)

Next, the probability of finding a blue marble >> 7 B's = 7/16
cross- multiply the red and blue's possibilities 1 over 4 × 7 over 16 = 7 over 64
yay, now that's your probability for part A

Part B >> again you have 4 over 16 (4/16)  or 1 over 4 (1/4) as your probability for red marble . . 
Next, what is your probability of selecting a blue marble with A RED MARBLE removed. 7/15 << take one red marble to get that 15 instead of 16. 
Now .. final part in this .. you gotta Multiply the probabilities
1 over 4 (1/4) × 7 over 15 (7/15) evaluate that for your answer

C. it wouldn't be equivalent, so No