Since we have 4 terms, we will assume a third degree polynomial for the nth term, because a third degree polynomial has four coefficients. That is, we assume a virtual function of the form Y = A*N^3+B*N^2+C*N+D Substitute these for (N,Y) (1,22), (2,59), (3,120), and (5,358) A*1^3+B*1^2+C*1+D = 22 A*2^3+B*2^2+C*2+D = 22 A*3^3+B*3^2+C*3+D = 22 A*5^3+B*5^2+C*5+D = 358 And solve the augmented matrix:We solve that matrix and get A = 1.83333333 B = 1 C = 21.16666667 D = -2 Then we substitute X=4 in Y = A*N^3+B*N^2+C*N+D and get 216. Edwin