6 : 21 : : 3 : ?

Select the option in which the numbers share the same relationship01 as that shared by the given pair of numbers.
72 : 108

72 : 18 : : 56 : ?

7 : 48 : : 12 : ?

212 : 436 : 560 : ?

248 : 3 : : 328 : ?

Select the option that is related to the third term in the same way as the second term is related to the first term.
$$ {7\over {50}}:{9\over {82}}:: {13\over170}:?$$

365 : 90 : : 623 : ?