Answer
180
Work Step by Step
The number of permutations of n items, where p items are identical, q items are identical, r items are identical, and so on, is given by:
$\frac{n!}{p!q!r!}$
The number of distinct ways the letters of the word DALLAS can be arranged:
$\frac{6!}{2!2!}$ = $\frac{6*5*4*3*2*1}{2*1*2*1}$ = 180 ways