Take into account that the each side of the rhombus has the same length, then, each side has the following length:

moreover, consider that segment EG is one diagonal of the rhombus, then, use the following formula to get the length of EG:
![EG=s\sqrt[]{2+2\cos \theta}](https://img.qammunity.org/2023/formulas/mathematics/college/nupdqbcc2ey0ohb9fr2l32mmluprzy42f6.png)
where θ = 70.
Replace the values of θ and s into the expression fro EG:
![EG=8\sqrt[]{2+2\cos 70}=13.10](https://img.qammunity.org/2023/formulas/mathematics/college/hts937zejt9yvnvrddqw9r7bb72xe00lyk.png)
by comparing with the given answer choices, you can conclude that the closest length is 15.