A function, \(y\), of \(x\) has gradient \(4x - 3\) at the point \((x,y)\) and the minimum value of the function is \(-\tfrac{1}{8}\). Express \(y\) in terms of \(x\) and sketch the graph of \(y\) against \(x\).

A function, \(y\), of \(x\) has gradient \(4x - 3\) at the point \((x,y)\) and the minimum value of the function is \(-\tfrac{1}{8}\). Express \(y\) in terms of \(x\) and sketch the graph of \(y\) against \(x\).