I think the answer is 15x^4y^5z^2
12a + 6 + 3a = 15a + 2
15a = 15a - 4
0 = - 4
Answer:
I believe your answer would be 
Step-by-step explanation:
Take 510, divide it by 30.
510/30 = 17
This means, every 17 red blood cells, there is 1 platelet, or 
Hope this helps! - Zac