The 'Anti Golput' convection company which is engaged in the sale of t-shirts and screen printing, has an investment plan to purchase 20 laser screen printing machines with a total cost of 75,000. In its current condition, the company incurs a screen printing fee of 25,000 per year. Meanwhile, after having 20 laser screen printing machines, the company is estimated to be able to save 60% of screen printing costs per year. It is also known that the company's internal rate of return is 15%. Determine the value of the payback period of this investment.