L.C.M of 3,24 and 8 is 24
The goal here is to make all the denominator equal to the L.C.M in this case it is 24.
24/3 = 8,
so multiplying both numerator and denominator by 8 won't change the fraction, i.e 14/3 = (14*8)/(3*8) = 112/24
but the advantage we gain by doing this that the denominator of 14/3 has now become 24.
Similarly for 121/24, but here the denominator is already equal to 24, so we have nothing to change.
But again, for 15/2, the denominator is 2 but we wish to make it 24, so we have to multiply both numerator and denominator
by 12. Because 24/2=12.