Mary's salary is $X per annum. The tax system is such that Mary pays a 15% flat rate of income tax on her salary. The tax system is due for reform, and politicians have suggested the following: Any income under $7,500 should be tax free. Any income above $7,500 should be taxed at 25% on the amount over $7,500. Given that Mary will be paying exactly the same amount of tax under both systems, calculate the amount of tax that Mary pays.