Zero-noise extrapolation with Richardson weights

A two-qubit circuit $U$ is run as $U$, $U(U^\dagger U)$ and $U(U^\dagger U)^2$, which multiplies its gate noise by the scale factors $\lambda=1,3,5$. With many shots per circuit the measured expectation values are

$E(1)=0.80,\qquad E(3)=0.56,\qquad E(5)=0.40.$

Assume the noise model $E(\lambda)=E_0+a_1\lambda+a_2\lambda^2+O(\lambda^3)$ and estimate $E_0$ by Richardson extrapolation through all three nodes,

$E_0\approx\sum_{i=1}^3\gamma_iE(\lambda_i),\qquad\gamma_i=\prod_{j\ne i}\frac{\lambda_j}{\lambda_j-\lambda_i}.$

Enter $E_0$. The value is graded with absolute tolerance $10^{-3}$; exact expressions such as 15/80.8-5/40.56+3/8*0.4 are accepted.