When you are trying to decide if a line represents a line of symmetry you can think about folding the figure across that line. Once you make the fold, do all of the parts line up on top?

If yes, then the line represents a line of symmetry.

If no, then the line does not represent a line of symmetry.

This line represents a line of symmetry because if you fold on the black line, then one side would lay on top of the other and the parts would match up.

We have the perimeter and the width, so we can plug those values into our equation and solve for our unknown.

Subtract from both sides

Divide by both sides

To find the value of x we subtract.