Given: 3x + y = 1.. solve for y.. y = -3x + 1. y = -3x - 1. y = 3x - 1

3x +y = 1
Subtract 3x from each side to find y, as follows:
y = -3x + 1
The first choice is correct.

The answer to the question given 3x + y = 1, to solve for y in the other given y=-3x + 1, y = -3x -1 and y = 3x -1. This is the following steps for the equation:
Step 1: add both sides with -3x to get  3x - 3x + y = 1 - 3x. the (3x - 3x) is equals to zero getting the equation of y = 1-3x.