Find the value of constant to determine the exact equation of the line. Suppose the line with the slope 1/10 goes through the point (5,5). Substituting the value of x and y in the equation y = 1/10x + b gives 5 = 1/10 * 5 + b. Solving for b gives b = 5 - 0.5, which equals 4.5. The equation of the line, therefore, is y = 1/10x + 4.5.
Substitute x with zero in the equation of the line to find the y-intercept. In this case, substituting x = 0 in the equation y = 1/10x + 4.5 gives y = 4.5. Note that it is always equal to the constant term.
Write the coordinates of y-intercept. In this example, it is (0, 4.5).