You need to simplify the equation. Because you can only add numbers with same variable, add 2x and x together to get 3x. Since 3x and -4y have different variables, they can't be added together, so this is the simplest form of the equation. JUST TO BE CLEAR, you won't be able to find the exact value of the variables unless you have more information. Therefore the only thing you can do is simplify.
![-2= \sqrt[3]{x+9}](https://tex.z-dn.net/?f=-2%3D%20%5Csqrt%5B3%5D%7Bx%2B9%7D%20)
![7=9+ \sqrt[3]{-17+9}](https://tex.z-dn.net/?f=7%3D9%2B%20%5Csqrt%5B3%5D%7B-17%2B9%7D%20)
![7=9+ \sqrt[3]{-8}](https://tex.z-dn.net/?f=7%3D9%2B%20%5Csqrt%5B3%5D%7B-8%7D%20)
