question on quadratic expansion

Question

I have been trying to solve this question, but no luck so far, any help would be appreciated.

Let $a,b,c > 0$ be such that $a^2 + b^2 -2bc =100, \ 2ab -c^2 = 100$. Then the value of $\dfrac{a+b}{c}$ is: ...

(the options are $10$, $100$, $2$, $20$)