Section 20. If the mortgagee or person claiming or holding under him has had possession of the land, he shall account for rents and profits, and be allowed for all amounts expended in reasonable repairs and improvements, for all lawful taxes and assessments paid and for all other necessary expenses in the care and management of the land. A balance of such account, if due from him, shall be deducted from the debt due on the mortgage; if due to him, shall be added to the debt, and paid or tendered as such.