Hey there, and good morning to you! :D
The perimeter is the sides added up. If you were to double each side, you would basically just get a perimeter that is 2 times bigger, since everything was doubled. A rectangle's length and width are the same as saying their sides. Width is the bottom or top, and the length is the sides.
30 x 2= 60
"C" 60 is your answer.
I hope this helps!
~kaikers