How do you factor 49t^2 - 81s^2?

Can be: $\left(7 t + 9 s\right) \left(7 t - 9 s\right)$
${a}^{2} - {b}^{2} = \left(a + b\right) \left(a - b\right)$
$49 {t}^{2} - 81 {s}^{2} = \left(7 t + 9 s\right) \left(7 t - 9 s\right)$