Numerical Methods: Euler to Runge–Kutta · Hard problem

The problem $y' = y^2$, $y(0) = 1$ has exact solution $y = \dfrac{1}{1 - t}$. Use two Euler steps with $h = \dfrac{1}{4}$ to estimate $y\left(\dfrac{1}{2}\right)$, and find the error (exact value minus Euler value). Express your answer as a common fraction.