There's not really a question here; let's explain.
When we add or subtract fractions, we need a common denominator to make the fractions compatible, so we can just add the numerators.
The common denominator often chosen is the Least Common Denominator, which is the Least Common Multiple of the denominators. To add fractions any common denominator will do; using the least common denominator helps keep the numbers small.
Here we have three fractions with denominators 30, 5 and 6 and we seek the least common multiple, the smallest number that's a multiple of all three. It's not going to be any smaller than the largest number on the list, 30, here. Since 30 is a multiple of 5 and 6, we've found our least common denominator.
It looks like the app used the factorizations to do the LCM calculation. First we break each number into prime factors:
30 = 2 × 3 × 5
5 = 5
6 = 2 × 3
To get the LCM we need enough of each prime factor so that each number divides the result. So we find the maximum exponent for each prime factor; that's the factor in the LCM.
This one isn't very interesting; the factors are 2,3 and 5; they never appear with an exponent higher than 1, so the LCM is 2 × 3 × 5 = 30.
