How can jane show appreciation to her mother

Gretta needs a $300,000 mortgage and is offered two choices. the monthly payments for the fixed rate and predicted payments for the arm are shown. adjustable rate mortgage year monthly payment 1-15 $1,610.46 adjustable rate mortgage year monthly payment 1-5 $1,520.06 6-15 $1,728.54 what is the difference between the total costs of the mortgages rounded to the nearest hundred? $8,700 $1,700 $15,800 $5,000

Idon’t understand 8. plz ! we are finding the area of polygons. thx in advance!

How do you do this? i’ve marked the correct answer but i can’t seem to calculate