whats the LCD of both of these fractions, and what is the equivalent fraction for each fraction? is it <, >, = please help

7/12, 11/18

- 11/20, - 22/40

15/28, 4/7

5/17, 15/51

whats the LCM of the numbers

7, 21

15, 50

28xy^2, 42x^2y

im sorry its so much, if u cant do it all i understand thanx any way, you're a big help!:D