Alemon with mass 0.3 kg falls out of a tree from a height of 1.8 m. how much mechanical energy does the lemon have just before it hits the ground? (assume there is no air resistance.)

Mechanical energy is the energy that is possessed by an object due to its motion or due to its position. It can either be kinetics or potential. In this problem you know it starting position so you can calculate it's potential energy (PE):

PE=mass∗gravity∗height=0.3kg∗9.8m/s2∗1.8m=?

The answer will typically be given in joules:

1J=kg∗m2s2 Could be wrong...  But I believe it is 5.3...? as a final product.