Elon Musk offers to buy Twitter for $54.20 a share.

The 54 percent premium over the share price on the day before Musk began investing in the company was what he said his offer to buy was. Credit... Pool photo by Patrick.

Just weeks after becoming the social media company's largest shareholder, Musk launched a takeover bid for it.

The best and final offer was a 54 percent premium over the day before Mr. Musk began investing in the company, according to a Securities and Exchange Commission filing. The company would be worth $43 billion.

In the filing, Mr. Musk said that he couldn't make the changes he wanted in the public market.

If the offer is not accepted, Mr. Musk would need to reconsider his position as a shareholder. I will open it.

The shares were higher in premarket trading. The closing price on Wednesday was $45.85. Morgan Stanley is Mr. Musk's financial adviser.

On April 4, a regulatory filing revealed that Mr. Musk had bought a 9.2 percent stake in the micro-messaging service. The next day, Mr. Musk accepted the offer to join the board but by the end of the week he turned it down.

Mr. Musk wrote to Mr. Taylor that he believed free speech was a societal imperative for a functioning democracy.

He realized that the company will not thrive or serve this societal imperative since he made his investment.

Since April 1, Mr. Musk's investment has become public.