Answer: D. 19
Let x by the length of CG. Since the two bases are parallel, we can create the following equation using proportions:
[tex]\dfrac{63}{21}=\dfrac{57}{x}[/tex]
Simplify left side of equation
[tex]3=\dfrac{57}{x}[/tex]
Multiply both sides by x
[tex]3x=57[/tex]
Divide both sides by 3
[tex]x=19[/tex]
Let me know if you need any clarifications, thanks!
