A two$-$dimensional simply$-$supported truss is subjected to forces at joints B and $F,$ as in the figure below.

straints $=5$

$($a$)$ Argue that the truss is statically determinate.

$($b$)$ Determine the external reactions.

$($c$)$ Use the method of joints to determine the internal forces of truss members $CF$ and $EF.$

$($d$)$ Use the method of sections to determine the internal force of truss member $BC.$