Here, A Refers to the long run value of the expense; P refers to the principal amount of money for being invested; r refers back to the fee of curiosity; n refers to the volume of instances the curiosity receives compounded yearly; t refers back to the tenure (in decades) https://www.google.com/maps/d/u/0/viewer?mid=1o3vHoDG_5EIkMXyD_8nuLLiHqxZbkJg