1.875g + 1.675g = 3.55g
2.00g of NH3 reacts with 2.50g of O2
2.00g + 2.50g = 4.50g
3.55g does not equal 4.50g ;_;
*EDIT* never mind I got it. I just added the left over NH3 that didnt react which is equal to about .9367g and it equaled to about 4.50. thank you to everyone who helped. i appreciate it