2.26: Sine curve constants and tangent sketch

The curve $y = a\sin bx + c$ has a period of $180^{\degree}$, an amplitude of $20$ and passes through the point $(90^{\degree}, -3)$. Find the value of each of the constants $a$, $b$ and $c$.

The function $g$ is defined, for $-135^{\degree} \le x \le 135^{\degree}$, by $g(x) = 3\tan\tfrac{x}{2} - 4$. Sketch the graph of $y = g(x)$ on the axes below, stating the coordinates of the point where the graph crosses the $y$-axis.