A print that large is going to be viewed from quite a distance so it wouldn't have to be printed at 300 PPI. You could probably get away with 150-200 PPI, so do the math.
150 PPI would be 6750 pixels in each direction.
200 PPI would be 9000 pixels in each direction.
If you think you need more or less you could calculate accordingly.
Thanks for helping Jim.
My friend wants it for her bedroom, so it won't be from a distance. Hence I'm a bit worried it will be pixelated if I don't get the settings right.
Maybe she should consider a smaller print.
Jim. Have you never dealt with a woman............ You ALWAYS agree with them.