Answer:
D
Step-by-step explanation:
Since you are trying to make x on its own, you are trying to get rid of the co-efficient. The co-efficient is three, so you divide 3 by 3, which would equal one, leaving x on its own. Whatever you do to one side you do to the other, so you would divide 27 by 3 as well.
x = 9
The perimeter of ABCD is 10, therefore, AB+AD=half of 10=5
the perimeter of ABD is 8, therefore, BD=ABD-(AB+AD)=8-5=3
3cm is the answer.
