Standard form is Ax + By = C where A and B are coefficients to x and y respectively.
We have to move things to the other side of the equal sign to get the standard form, keeping in mind that the sign changes after it crosses over
Y = 1x + 3
We move the y to the right side
1X + 3 - Y = 0
Then we move the constant over
1X - Y = -3
The standard form of 1x + 3 = y is 1x - y = -3