Provide your best answer for the following math problem. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The problem is: jacob is 39 years old . he is 3 times as old as his brother . how old will jacob be when he is twice as old ?
65
jacob will be 78 years old.