Question: unable to compute

hello, i'm trying to rewrite the RiemannSum function, it's for my homework, 

i wrote the entire fonction, but looks like my function is not evaluated, i don't understand why!!! if anyone could see what's wrong please let me know, thanks. here is  my piece of code, and i also attached the file

> with(Student[Calculus1]);

> with(plots);

> with(plottools);

> f(x):= (1)/(5.6 sqrt(2 Pi))*exp(-((x-169)^( 2 ))/(2(5.6)^(2)));

SR:=proc(a, b, f, n) description "Les sommes de Riemann";  local Delta, x,SR,xetoile, i;  Delta:= (b-a)/(n);  for i from 0 to n by 1 do  x(i):= a + i*Delta;  end do;  for i from 1 to n by 1 do  xetoile(i):= (1)/(4)(x(i) + 3 x(i-1));  end do;  SR := 0;  for i from 1 to n by 1 do  SR := SR + f(xetoile(i))*Delta;  end do;  return SR  end proc;

if i compute the procedure SR(0, 150, f(x), 10), it doesn't give a result