This question isn't very specific. Are we assuming that this is a right triangle and calculating the hypotenuse.
I'm going to guess not, because the hypotenuse is clearly the longest length, and all the choices are not above 10.
So, what this means is we are calculating B.
We make the equation:
7
![7^2+b^2=10^2](https://img.qammunity.org/2019/formulas/mathematics/middle-school/apdyxk55niayqf9bj67lppedealhld9at6.png)
From here, we solve and get:
![49 + b^2 = 100 \\ 100-49 = b^2 \\ 51 = b^2 \\ √(51) \\ b = 7.14](https://img.qammunity.org/2019/formulas/mathematics/middle-school/hmk5zphvkjpl5cmvhnx6uozu71ios7gpea.png)
So, clearly this is not an option.
Is there any additional information provided? Is it a special triangle?
This would be right if it was a right triangle. Let me know if I wrong in the comments.