Answer:
\(a=6\ m\)
Step-by-step explanation:
Here,
\(m\angle A=18^{\circ}\\\\m\angle C=21^{\circ}\\\\AB=c=7\ m\\\\BC=a=??\)
Sine law-
\(\dfrac{\sin A}{a}=\dfrac{\sin B}{b}=\dfrac{\sin C}{c}\)
Putting the values,
\(\Rightarrow \dfrac{\sin 18}{a}=\dfrac{\sin 21}{7}\)
\(\Rightarrow a=\dfrac{\sin 18\times 7}{\sin 21}\)
\(\Rightarrow a=6\ m\)
