Alright. One way you can do this is to list multiples of each denominator:
1/4:
4, 8, 12, 16, 20, 24, 28, 32, 36...... and so on
3/7:
7, 14, 21, 28, 35, 42, 49, 57, 63......
1/11;
11, 22, 33, 44, 55, 66, 77, 88......
Keep going until you see the least common denominator!
Now an easier way to do this is by multiplying all of the numbers in the denominator then get the factors:
4*7*11 = 308
And since those are not divisible by a whole number (besides 4 but 308 won't be divisible by 2*7*11)
Therefore 308 is the least common denominator.
