we know that GCF of fraction = (GCF of numerator) / (LCM of denominator)
therefore GCF(x/2,y/2) = GFC(x,y) / LCM(2,2)

1) from statement 1: we know that GCF(x/2,y/2) = 5
2) LCM of 2,2 = 2

therefore
5 = GCF(x,y) / 2
hence, GCF (x,y) = 10

A is sufficient $$$$