When you find yourself struggling to come up with a solution or answer, you may say that you need to "rack your brains". However, there are a number of alternative phrases that you can use to convey the same meaning. For example, you might say that you need to "put on your thinking cap", "wrestle with a problem", "mull over an issue", or "deliberate on a matter". You might also say that you need to "apply yourself", "work towards a solution", or "try to figure things out". Whatever phrase you choose to use, the meaning is the same: you're trying to come up with a solution by thinking deeply about a problem.