Charge $1(0\mathrm{.}15$ kg$)$ in the following diagram is hanging from a light insulating thread, as shown. Charge $2$ is brought close and pulls charge $1,$ deflecting the string away from the vertical axis. The charges have the same magnitude, but charge $1$ is negative.

a$)$ Find the tension in the thread. $(2$ marks$)$

b$)$ Find the charge on $2.$ Is it positive or negative? Explain your reasoning. $(4$ marks$)$