Answer
20.8 g $NCl_{3}$
Work Step by Step
$3NaClO+NH_{3}$ -> $NCl_{3}+3NaOH$
Mass of $NCl_{3}$ = $\frac{(2.94gNH{3})\times(1molNH_{3})\times(1molNCl_{3}}{(17.04gNH_{3})\times(1molNH_{3})\times(1molNCl_{3})}$
$\approx$20.7663380…
=20.8 g $NCl_{3}$