Answer:
6 units
Step-by-step explanation:
The questions states that the area = perimeter.
From this we can set up an equation:
[tex]x*y=2x+2y[/tex]
Since we know one of the sides is 3 we can substitue one of the variables for 3. In this case I choose [tex]y[/tex]
[tex]3*x=2x+2*3\\3x=2x+6[/tex]
Solving for x we get [tex]x=6[/tex].
That's our answer!
