Find f(a-2) when f(x)=x^2-1
i forgot how to do these so show all steps

Margaret is purchasing a house for $210,000 with a 15 year fixed rate mortgage at 4.75% interest she has made a 5% down payment the house is valued at 205,000 and the local tax rate is 3.5% homeowners insurance 600 per year what are her total monthly payment