Answer:
D
Explanation:
The perimeter of a rectangle is found using P=2l+2w. For this reactangle, l=3x since its 3 times the width. The width is just x.
Then the perimeter is P = 2*3x+2*x = 6x+2x=8x.
Answer D is the correct choice since x+3x+x+x+3x = 8x.