Answer:
D.
Step-by-step explanation:
Its given that the rectangle has a perimeter of 60 units. A rectangle has four sides, and to get the perimeter, you add up all four sides. You are given one side is 20 units, and the other as 'x.'
So,
x + x + 20 + 20 = 60
2x + 40 = 60
Example for *wrong* answer:
Letter C, x + 20 = 60, that would'nt equal 60 because youre only adding two sides instead of all four.
Hopefully this helps :)