a) 12 (6x2),(4x3),(3x4)
b) 12 (4x3),(3x4),(2x6)
c) 20 (10x2),(5x4),(4x5)
*A way to solve these questions is always to start with the largest number and start multiplying that number by 1 to see if it could be a LCM and then move to multiplying the biggest number by 2, and so on, until you get an answer that satisfies all the other numbers.