Answer: C) 30 units
We can solve this problem by adding all of the sides that we know the length of. By counting the units of the vertical and horizontal sides, we get 20 units. Then, to find the length of the diagonal side, we can use the pythagorean theorem. We can form an imaginary triangle with the diagonal side as the hypotenuse. The lengths of the bases are 6 and 8. Then we can use the formula for pythagorean theorem to find the length of the hypotenuse, as follows:
6^2 + 8^2 = c^2
36 + 64 = c^2
100 = c^2
c = 10
Then we can add this length to our earlier length of 20 units to find the total perimeter of the quadrilateral.