Answer:
![10x^(2)-34](https://img.qammunity.org/2020/formulas/mathematics/high-school/2h7w1a3u7w61da4z3zxa28nlog90ucqke0.png)
Explanation:
Because we are told equivalent expressions for y and z we can plug those in to 2(y+z).
![2((3x^(2)+x^(2)-5)+(x^(2)-12))](https://img.qammunity.org/2020/formulas/mathematics/high-school/t8mk2347irrg6rgj5bwloat19v619k4kog.png)
Then simplify by combining like terms of the expressions. Values ending in x^2 can be combined with each other.
![2(5x^(2)-17)](https://img.qammunity.org/2020/formulas/mathematics/high-school/hbvc56v3hfukd14ecvs7sfbsajwm833193.png)
Now we can distribute the 2 by multiplying each value in the parentheses by 2.
![10x^(2)-34](https://img.qammunity.org/2020/formulas/mathematics/high-school/2h7w1a3u7w61da4z3zxa28nlog90ucqke0.png)