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