Fourier Coefficients and Signal Recostruction

The two picture above are the question I am being asked and some background. I have been on this problem for close to 2 and a half hours. This is the code I have written so far. Any help would be greatly appreciated.

T=2;
To=4;
Dt=.01;
t=-5:Dt:5;
N=10;
n=1:1:N;
ao=(T/To);
fo=1/To;
x1=zeros(10,1);

for n=1:10
   an=(1/(pi*n))*sin((n*pi*T)/To);
   x1(n+1)=(an)*cos(2*pi*n*fo*t);

end
gt=ao+2*x1(n+1); 
ggt=gt*Dt;
plot(t,ggt);

      % code
    end