In Fig. $37-9$, observer $S$ detects two flashes of light. A big flash occurs at $x_{1}=1200 \mathrm{~m}$ and, $5.00 \mu$ s later, a small flash occurs at $x_{2}=700 \mathrm{~m} .$ As detected by observer $S^{\prime}$, the two flashes occur at a single coordinate $x^{\prime}$. (a) What is the speed parameter of $S^{\prime}$, and (b) is $S^{r}$ moving in the positive or negative direction of the $x$ axis? To $S^{\prime}$, (c) which flash occurs first and (d) what is the time interval between the flashes?