How do I find the equation of a straight line from a graph?

Let's use a general equation for straight lines, y= mx +c. Here, the m and c represent numbers (or constants), which will differ for each specific line. The number in the place of the m is the gradient of the line, or the slope. This is calculated by dividing the change in height along the y axis by the change in width along the x axis (sometimes called rise over run). The number in the place of the c is where the straight line crosses the y axis. If I draw an example, such as this graph, we can see that for each x coordinate that increases we go up 2 y coordinates, so our slope is 2/1=2 which we substitute for our letter m. We can also see that the line crosses the y axis at the number 1, so that is what we plug into our letter c, giving us the equation. y=2x+1