What is the area of rhombus abcd ? enter your answer in the box. do not round at any steps.

Calculate the length of AB
c = √(36+9) = 3√5
Calculate the length of BC
a = √(36+9) = 3√5
Calculate the length of AC.
b = √(0+36) = 6

Calculate the perimeter of ΔABC
p = 6√5 + 6
Half the perimeter is
s = 3 + 3√5
s-a = 3
s-b = 3√5 - 3
s-c = 3

Note that
 (3√5 + 3)(3√5 - 3) = 45 - 9 = 36.

Calculate the area of ΔABC.
A = √[(3√5 + 3)(3)(3√5 - 3)(3)]
   = 3(6)
   = 18

The area of the rhombus is twice the area of ΔABC, so it is 36 units².

  36