Answer:
FG = 15
Step-by-step explanation:
Note that
EF + FG = EG ← substitute values into equation, that is
6 + FG = 21 ( subtract 6 from both sides )
FG = 21 - 6 = 15

![\\ \sf{:}\implies side=\sqrt[3]{14}](https://tex.z-dn.net/?f=%5C%5C%20%5Csf%7B%3A%7D%5Cimplies%20side%3D%5Csqrt%5B3%5D%7B14%7D)

Now

Cut it into 10 parts as per question(Open side means five sides hence it will be 5×2=10)

Now divide by previous side

Option D