use Scheme

4. (3 points) Write a higher-order function ncall that takes three pa- rameters: n, f, z; it returns when n = 0, returns f(z) when n = 1, returns f(f(x)) when n = 2, etc. That is, it returns the result of calling f on x, for n times. For instance, invoking ncall with n = 4, the add-one function, and x = 2 should return 6