The form of the linear equation is

m is the slope
b is the y-intercept
Since the slope of the line is 1, then
m = 1
Substitute it in the form of the equation above

To find b substitute x and y in the equation by the coordinates of a point on the line
Since the line contains the point (4, 1), then put
x = 4 and y = 1

Subtract 4 from both sides to find b

Substitute the value of b in the equation

The equation of the line is y = x - 3