how do you take the l.c.m of more than two fractions

As an example:   108     45     480

First, factor each number, using exponents:  

        108  =  2² · 3³          45  =  3² · 5          480  =  2⁵ · 3 · 5

Now, take each factor, with its largest exponent.

   ---   the largest exponent on 2 is 5, so use 2⁵

   ---   the largest exponent on 3 is 3, so use 3³

   ---   the largest exponent on 5 is 1, so use 5

Multiply these together:     2⁵  · 3³ · 5   =   4320