Need help on a code part for signal processing.

Hello everyone i have an exercise for signal processing course im taking and our homework's solution is this code. Looking at the graphics i can confirm this answer is true. But I'm having a hard time to understand some parts of the graphics.

%matlab
ts=0.0001;
to=0.1;
t=0:ts:to;
m=sinc(100.*t);
fc=250;
c=cos(2*pi.*fc.*t);
u=c.*m;
subplot(211);
plot(t,m);
xlabel('t');
ylabel('m(t)');
subplot(212);
plot(t,u);
xlabel('t');
ylabel('u(t)');
f=linspace(-1/(2*ts),1/(2*ts),length(t));
M=fftshift(fft(m))./length(t);
U=fftshift(fft(u))./length(t);
figure
subplot(211);
plot(f,abs(M));
xlabel('f');
ylabel('|M(f)|');
subplot(212);
plot(f,abs(U));
xlabel('f');
ylabel('|U(f)|');

so this is the solution to my code. this code provides me these graphics.

Look at figure 2. U(f) and M(f) is between (0-0.06) and (0-0.08), respectively. If i change the T0 to 0.4 like this;

ts=0.0001;   to=0.4;   t=0:ts:to;

U(f) is between 0-0.015 and M(f) is between 0-0.03. can anyone tell me what causes these changes. The only part i didn't understand from the code. thank you all of you for your time.