What is the key endogenous variable in the quantity theory? Explain the effect on this key variable of the following changes:

What is the key endogenous variable in the quantity theory? Explain the effect on this key variable of the following changes:

What is the key endogenous variable in the quantity theory? Explain the effect on this key variable of the following changes:
A) The money supple is doubled.

B) The velocity of money increases by 10%.

C) Real GDP rises by 2%/

D) The money supply increases by 3% while real GDP rises by 3% at the same time.