Answer: 
Step-by-step explanation:
For this exercise you need to remember:
1) The mulitplication of signs:

2) By definition, like terms contain the same variables with the same exponent.
Then knowing this, and given the equations:
and 
You must subtract the like terms, which means that you must subtract the numerical coefficients of each term.
Then, you get the result is:

4/7 of a chance. There are a total of 14 cars. 6 are yellow. 8 are not. 8/14 of the cards are not yellow. 8/14 simplifyed= 4/7.
1. x = 2
2. x = 9
3. a = 3
4. x = 13
5. c = 3
6. s = 3
7. x = 7
8. c = 0
9. b = 1
10. c = 4
11. x = 4
12. x = 8
13. x = 12
14. y = 10
15. x = 11
16. x = 10
17. x = 6
18. x = 11