Respuesta :

3NH₃ + H₃PO₄ ======> (NH₄)₃PO₄

1.8 / 98 = 0.018367Mol of phosporic acid

it's a 1:1 ratio 0.08367 x RFM of ammonium phosphate (149) = 12.46g 

hope that helps :)
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