Given the ratios of the exradii \(r_1 : r_2 = 3 : 4\) and \(r_1 : r_3 = 2 : 3\).
Using the formula for exradii:
\[
r_a = \frac{\Delta}{s - a},
r_b = \frac{\Delta}{s - b},
r_c = \frac{\Delta}{s - c},
\]
where \(s = \frac{a+b+c}{2}\) is the semiperimeter.
From the given ratios,
\[
\frac{r_1}{r_2} = \frac{s - b}{s - a} = \frac{3}{4},
\frac{r_1}{r_3} = \frac{s - c}{s - a} = \frac{2}{3}.
\]
From these, express \(s - b = \frac{3}{4}(s - a)\) and \(s - c = \frac{2}{3}(s - a)\).
By solving these simultaneous equations, and considering \(a, b, c\) are related to \(s\), the side lengths ratio \(a : b : c = 5 : 6 : 7\) is obtained.