Sketch the following Signal: $x(t)=3\sin(\frac{\pi t}{4})$
From your physics knowledge you get that sine waves are usually equated, in the general case, as 

$$y(t) = A * \sin(\omega t)$$

where $\omega = 2 \pi f$ and the periodicity is $T=1/f$

Comparing the general equation with your particular case, you have: $$2*\pi*f = \pi / 4$$
meaning that $$f=1/8 Hz$$
or $$T=1/f=8s$$
The amplitude is $A=3$

If you want to plot it in matlab, for example, just write

t = 0:0.01:16;
x = 3*sin(pi*t/4);
plot(x,t)


As a final comment, this is really a basic question and you should carefully read your textbook if you want to progress to more advanced topics.