A non-ideal spring exerts a restoring force whose magnitude increases quadratically with stretch according to \(F(x) = bx^2\), where \(b\) is a positive constant and \(x\) is the displacement from equilibrium. The graph of the applied force required to stretch the spring as a function of \(x\) is shown. An external agent does an amount of work \(W_1\) to stretch the spring from \(x = 0\) to \(x = d\), and does an additional amount of work \(W_2\) to stretch the spring further from \(x = d\) to \(x = 2d\). What is the ratio \(\dfrac{W_2}{W_1}\)?