Any line with a gradient of 3 will be parallel to \(y = 3x + 7\). Two examples ... equation for all straight lines, \(y = mx + c\). If \(y = 3x - 1\) the gradient of the graph is 3.

If an equation can be rearranged into the form \(y = mx + c\), then its graph will be a straight line. In the above: \(x + y = 3\) can be rearranged as \(y = 3 - x\) (which can be re-written as ...