Answer & Step-by-step explanation:
The formula is given in the middle. You are supposed to insert the value of x into this formula to find the value of y (like in the first given example):

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:Done
Add like terms. "Like terms" are those with the same constellation of variables.
.. terms with variable x: 5x +3x = (5 +3)x = 8x
.. terms with no variable: -9 -20 = -29
The simplified form is 8x -29.