To describe an objects position, you must first choose a reference point as a starting place. from there you must specify the

The question is not full.

But we must then specify in which direction do we want to be positive.

Explanation:

If we have to object moving up or down, object A and object B respectively.

If we choose up as negative, then object A is moving towards the negative position, if it is displaced by 21m, then is 21m in the negative direction.

The statement is the same for object, with the change in direction, in this case, it will be positive.  

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.