Length

[kenhkelly]

Closes #642

• [x] Running yarn lint does not trigger any linter errors
• [x] The test of the method you have fixed is passing
• [x] You have written a new skeleton method for someone else to work on!
• [x] You have written tests to accompany your skeleton method

[kenhkelly]

@ktilcu I updated the test string

[ktilcu]

@kenhkelly Thanks! Though, I think this is the perimeter of a triangle. If you wrap that up we can get it done.