You have the following expression:
7y + 3x + 7z - 2x + 4 - x
In order to simplify the previous expression, consider that you only can simplify like terms (terms with the same variable and with the same exponent).
Order the expression as follow:
3x - 2x - x + 7y + 7z - 4
Next, simplify like terms (simplify coefficients and put the same variable):
3x - 2x - x + 7y + 7z - 4 = 3x - 3x + 7y + 7z - 4 = 7y + 7z - 4
Hence, the result is:
7y + 7z - 4
