w2-169=0
36a2= 169
15t2-11t-12= 0
$\displaystyle 36a^2=169$
Take the square root of both sides.
$\displaystyle \sqrt{36a^2}\ = \sqrt 169$
$\displaystyle 6a=13$
$\displaystyle a= \frac{13}{6}$
For the other one, you can factor it.
$\displaystyle 15t^2-11t-12 = (3t-4)(5t+3)$
And from there, it's easy to solve.