Article: In 1886, Woolwich munitions workers founded the club as Dial Square. In 1913, the club crossed the city to Arsenal Stadium in Highbury. They became Tottenham Hotspur's nearest club, commencing the North London derby. In 2006, they moved to the Emirates Stadium in nearby Holloway. Arsenal earned €435.5m in 2014–15, with the Emirates Stadium generating the highest revenue in world football. Based on social media activity from 2014–15, Arsenal's fanbase is the fifth largest in the world. Forbes estimates the club was worth $1.3 billion in 2015.

Now answer this question: How does Forbe's believe the Arsenal club was worth in 2015?
$1.3 billion