Evaluate the limits, using L'Hôpital's Rule.
Enter INF for $\infty$, -INF for $-\infty$, or DNE if the limit does not exist, but is neither $\infty$ nor $-\infty$.

a) $\displaystyle \lim_{x\to 0} \frac{\sin(4 x)}{\sin(10 x)} =$

b) $\displaystyle \lim_{x\to 0} \frac{\sin(a x)}{\sin(b x)} =$ (assuming $b \neq 0$)