Problem: Given $u_1 = 1, u_2 + u_3 = 6$ and $u_4 + u_5 + u_6 + u_7 + u_8 = 30.$ What is the approximate value of $u_4$ when computed by using Lagrange's interpolation formula?
I tried to solve it as described here: https://www.geeksforgeeks.org/lagranges-interpolation/
But unable to put the components together.