A company plans to phase out one model of its product and replace it with a new model. An advertising campaign for the product being replaced just ended, and typically after such a campaign, monthly sales volume S (in dollars) decays according to

S = 22,000e^-0.35t

where t is in months. When the monthly sales volume for this product reaches $2500, the company plans to discontinue production and launch the new model. How long will it be until this happens?