Please only if you know please Lena starts to use the standard algorithm to solve 39\times439×439, times, 4. Her work is shown below.
\begin{aligned} \overset{\blueD{m}}3\overset{}9&\\ \underline{{} \times \phantom{~~~~} 4}&\\ 6& \end{aligned}

35.0 units long.

Step-by-step explanation:

You can treat a rhombus as four right triangles, where there is a short side, a long side, and a hypotenuse.

The hypotenuse of a right triangle inside a rhombus will always be on the exterior.

To find the hypotenuse of one of the right triangles, use the Pythagorean theorem:

We are given that a = 9 and b = 15, but in order to get the values needed for the theorem, we must divide them by 2 in order to get the sides for the triangles.

9 / 2 = 4.5, 15 / 2 = 7.5

Then, you can substitute your values into the Pythagorean theorem:

Knowing that one of the external sides is 8.7464 units long, you can then multiply that value by 4 to get your perimeter, as there are four identical sides forming the perimeter:

8.7464 * 4 = 34.9856. Rounded: 35.0