When you add a positive and negative number does it equal a positive or negative

Can i get some on 18,20,& 22? or one of them

Amuffin recipe, which yields 12 muffins, calls for cup of milk for every 1 cups of flour. the same recipe calls for cup of coconut for every cup of chopped apple. to yield a batch of 30 muffins, how much flour will be needed in the mix?

If 3x+8=3x+8 is it one solution or no solution