Final answer:
The standard form of the linear equation 7x - 21 + 2y = 0 is 7x + 2y - 21 = 0.
Step-by-step explanation:
The standard form of a linear equation is in the form ax + by + c = 0, where a, b, and c are constants. In the given equation, 7x - 21 + 2y = 0, we can rewrite it in the form ax + by + c = 0 by rearranging the terms. So, the correct standard form of the equation is 7x + 2y - 21 = 0.