Consider the question. Sarah's age is equal to three times Mark's age minus 4. Mark is four years older than Billy. Billy is half Ana's age. If Ana will be 15 in 3 years, how old is Sarah?
 If the answer is '26'; explain the reasoning:
First figure out how old Ana is right now by subtracting 3 from 15: 15 - 3 = 12. Next, figure out how old Billy is by dividing Ana's age by 2: 12 / 2 = 6. Now figure out how old Mark is by adding 4 to Billy's age: 6 + 4 = 10. Now, to figure out Sarah's age, first multiply Mark's age by 3: 10 * 3 = 30. Finally, subtract 4 from triple Mark's age to find Sarah's age: 30 - 4 = 26.