ABC Manufacturing decides to build a new plant. The plant will cost £2 million immediately and is expected to have a useful life of 10 years. After 5 years, a significant renovation expense of £X will be required to install the new technology. The plant will produce level returns of £300,000 at the end of each year for the first 5 years and double that at the end of each for the second 5 years. 

Find the maximum value of X that ABC could pay that would still produce an internal rate of return on its investment of at least 12%.