You need at least two numbers to find an LCM.
The common denominator is 28.
A common denominator, though not the least, is 168.
A common denominator, though not the least one, is 14*49 = 686.
A common denominator, though not the least one, is 14*12 = 168.
There is none because the Least Common Denominator (or LCD) is the Least Common Multiple (LCM) of the denominators of a pair of fractions.
The least common denominator is 70.
You need at least one more fraction in order to have a common denominator.
There is none because the Least Common Denominator (or LCD) is the Least Common Multiple (LCM) of the denominators of two or more fractions.
7.
Their product.
98
168