A trader creates a long strangle with put options with a strike price of $60 per share, and call options with a strike of $70 per share by trading a total of 20 option contracts (10 put contracts and 10 call contracts). Each contract is written on 100 shares of stock. The put option is worth $9 per share, and the call option is worth $7 per share. Derive the profit of this position at maturity as a function of the then spot price.