Find the LCM by using prime factorization method:

$84,93,105$

If $\frac{1}{y+z}+\frac{1}{z+x}=\frac{2}{x+y}$ then what is the value of $x^2+y^2$? 

Find the LCM and HCF of $6$ and $20$ by the prime factorisation method.

Find the HCF of 3, 7 and 15. 

(A) 7 

(B) 15 

(C) 3 

(D) 1