(a(i))[2]
Show that the angle $BAF$ is $120^\circ$.
(a(ii))[3]
Use trigonometry to determine the length of $PQ$ in terms of $x$.
(a(iii))[3]
Show that the length $PS$ is $(20-x)$ cm.
(b)[4]
Use the results from part (a)(ii) and part (a)(iii) to determine the length of one side of the square.