Find the prime factorization of each:
136 = 2 x 2 x 2 x 17
204 = 2 x 2 x 3 x 17
340 = 2 x 2 x 5 x 17
Chose the highest number of times each factor is found in each number:
2 is found at least twice in each number, 17 is found at least once in each number.
Multiplify these factors 2 x 2 x 17 (Use 2 twice because it's found twice, use 17 only once.)
Find the prime factorization of each:
136 = 2 x 2 x 2 x 17
204 = 2 x 2 x 3 x 17
340 = 2 x 2 x 5 x 17
Chose the highest number of times each factor is found in each number:
2 is found at least twice in each number, 17 is found at least once in each number.
Multiplify these factors 2 x 2 x 17 (Use 2 twice because it's found twice, use 17 only once.)