How do you find the y intercept when you have the slope and a point?

The equation of a line can be written in a format called "point slope form". Equations in this form look like y - y1= m(x - x1). In this formula (x1,y1) is any point on the line, m is the slope, x is the input (or dependent variable) and y is the output or dependent variable. Using this, and a given slope and point, you can construct the equation for a line.

The y-intercept is the point where a line crosses the y-axis. You don't know where on the y-axis, but you know that the x-value of any point of the y-axis is 0. Therefore, you can solve for the y-intercept bus substituting 0 for x and solving for y.