Question

How do I find out how to work out , y=mx+c ???

Answer 1

Y=mx+c isn't an equation to solve. It's the slope-intercept formula for graphing lines.
y and x are the variables, and m and c are the constants.
As an example, the line y=4x+2 looks like this:

Answer 2

-assuming you meant y=mx+b-

To find slope, you first pick 2 coordinates and plug them into y2-y1 divided by x2-x1. After that you can pick a coordinate and multiply by the slope you got and if necessary, add a certain number to get the y-coordinate. Then, plug your values into y=mx+b with m for slope and b for y-intercept. IF YOU ARE JUST GIVEN AN EQUATION, change the equation into slope intercept form and just answer for m being the slope and b being the y-intercept.