The total ages of 2 buildings is 201 years. if one building is twice as old as the other, what are the ages of 2 buildings?

67 years and 134 years

In this case, you are given the buildings sum ages ( building A ages+ building B ages = 201 years) and the building ratio ( Building A ages= 2x Building B ages).
To answer the question, you simply need to insert the second equation into the first. It would be:

building A ages + building B ages= 201
2x building B ages + building B ages= 201
building B ages= 67 years.

Then building A ages= 2x 67 years= 134 years.