Limiting reactants not so sure how to do it plz help

Can someone me with 3 and 4 plz. this is for masteries test.

Aweight lifter raises a 1600 n barbell to a height of 2.0 meters. how much work was done? w = fd a) 30 joules b) 3000 joules c) 320 joules d) 3200 joules

The plant food contains nh4)3po4 what tests would you run to verify the presence of the nh4 ion and the po4 ion