Call the mystery number of years ' Y ' .
In 'y' years, Mr. Jacobs will be (55+y), and tony will be (7+y).
You said that Mr. Jacobs will then be 4 times as old as tony, so . . .
55 + y = 4 (7 + y)
Eliminate the parentheses: 55 + y = 28 + 4y
Subtract 28 from each side: 27 + y = 4y
Subtract 'y' from each side: 27 = 3y
Divide each side by 3 : 9 = y
In 9 years, Mr Jacobs will be (55 + 9) = 64.
In 9 years, tony will be (7 + 9) = 16.
64 is 4 times 16, and now that tony has turned 16,
he can start spelling his name with a capital ' T ',
like a regular grown-up.