Numerical Methods: Euler to Runge–Kutta · Hard problem

A problem is solved with the classical RK4 method (global error $\approx C h^4$). With step $h$ the computed value of $y(2)$ is $0.8412$; with step $\dfrac{h}{2}$ it is $0.8397$. Use Richardson extrapolation to give an improved estimate of $y(2)$. Express your answer as a decimal to four places.