If excess ammonium sulfate reacts with 20.0g of calcium hydroxide how many grams of ammonia are produced

The reaction between ammonium sulfate and calcium hydroxide is given below. 
            (NH₄)₂SO₄ + Ca(OH)₂ --> 2NH₃ + CaSO₄ + 2H₂O
From the balance equation, we can conclude that every 74 g of calcium sulfate reacted with enough amount of ammonium sulfate will yield 34 grams of ammonia. From the given amount,
               (20 g calcium sulfate) x (34 grams ammonia / 74 g calcium sulfate)
                               = 9.19 g ammonia

Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.