Answer:
Since the lease amount varies, we must calculate the annual rental income using the following formula:
annual rental income = {lease year 1 - (lease year 1 x 6/12) + [lease year 2(and beyond) x number of remaining contract years] / total number of contract years}
annual rental income = [$8,000 - ($8,000 x 6/12) + ($12,500 x 4)] / 5 years = {$8,000 - $4,000 + $50,000} / 5 years = $54,000 / 5 = $10,800