Lines, Angles, and Triangles

In the figure, lines $\\ell_1 \\parallel \\ell_2 \\parallel \\ell_3$. A transversal crosses all three lines. The segment between $\\ell_1$ and $\\ell_2$ has length 3 and the segment between $\\ell_2$ and $\\ell_3$ has length 4. Another transversal cuts the parallel lines such that its segment between $\\ell_1$ and $\\ell_2$ has length 6. What is the length of its segment between $\\ell_2$ and $\\ell_3$?