I only know (b) and 28 (c)
(b) Multiples of 120= 120,240,360,480,600
Multiples of 150= 150,300,450,600
Both numbers have 600 as their first common multiple so the ANSWER is 600
28. (a) Common factors of 24= 1,2,3,4,6,8,12,24
Common factors of 64= 1,2,4,8,16,32,64
8 is the only common factor for both 24 and 64 so 8 is the ANSWER