P = 18.4 units
Step-by-step explanation:
Sides AB and CD are congruent and thus have the same length.
Sides AD and BC are congruent.
The length of side AB is found using the Pythagorean Theorem:
|AB| = √ [ 5² + 1² ] = √26
and
|BC| = √ [ 4² + 1² ] = √17
Then the perimeter is P = 2(√26) + 2(√17), or
                      10.20   +  8.25, or, to the nearest tenth,
                   P = 18.4 units       Â