Mustang "The Brits originally asked North American to build a plane that would replace the outdated P-40. North American modeled the P-51 after the P-40. Which is why the P-40 looks somewhat like a P-51.
Mustang, the British did not ask North American to build a replacement aircraft for the P-40, they were asked if they could build the P-40 on licence. They said "we can build a better aircraft than the P-40" the British said OK go ahead, and the P-51 was born.
As for the statement that the P-51 "looks like" the P-40
What part of the P-40 looks like the P-51???