Add fractions

What number could be a common denominator for these two fractions?
1/5   and   5/6?

• 30
• 11
• 6
• 5

• 1/12
• 1
• 2/35
• 23/25

8/9 - 1/3 = 

• 7/6
• 5/9
• 2/3
• 8/27