Sarah is 30 years old.

She is twice as old as her friend Bill means Billy is 2 times younger than Billy:

Billy is 30/2 = 15 years old.

Bill is 5 times as old as his sister Jane means Jane is 5 times younger than Billy:

Jane is 15/5 = 3 years old.

Jane’s mom is 12 times older than Jane:

Jane's mom is 12*3 = 36 years old.

The age difference between Jane’s mom and Sarah is:

36 - 30 = 6 years.