3.24: Sine graph: find a, b, c

The diagram shows the graph of $y = a\,\mathrm{sin}\,bx + c$, where $a$, $b$ and $c$ are integers, for $-180^{\circ} \leqslant x \leqslant 180^{\circ}$. Find the values of $a$, $b$ and $c$.