If i have an image of approx 8.5MB (5000x2800 pixels) and want a print of approx 30x20, what ppi do i need ??

At 300, PS is telling me the image size is 16x9" , if I drop it to 150 ppi, it is telling me image size is 33x18"

Im a little confused, I dont normally print beyond about 18x12 (300ppi) so larger sizes im not real sure of.

Thanks in advance