Instead of jumping to the shortcut, build the full picture using a common multiple so every share comes out as a whole number.
Since T and B together are 3 times J, and J and B together are 4 times T, let the total money be a convenient multiple of 5, 4, and 3, say 60x. Because J+B is 4 times T, and J+B+T is the whole 60x, T's share solves as $60x = 4T + T = 5T$, so $T = 12x$. Then J+B = 48x. Using T+B = 3J: substitute B = 48x - J, giving $12x + 48x - J = 3J$, so $60x - J = 3J$, meaning $J = 15x$, and then $B = 48x - 15x = 33x$.
T's share of the total is $\frac{12x}{60x} = \frac{1}{5}$.
Let's summarize:
This confirms option D through the full simultaneous-equation build rather than the shortcut.