$3.$ Ammonium chloride is produced by reacting ammonia with hydrochloric acid. If a reaction yields $780$ kg of ammonium chloride, how much ammonia was used if the reaction efficiency is $88\%?$

$4.$ Calcium ammonium nitrate $($CAN$)$ fertilizer is applied at a rate of $100$ kg per hectare. If the nitrogen content in CAN is $27\%,$ how much nitrogen is being applied to each hectare?