You have to ask the printer:
Minimum resolution should be 240 to 300ppi but if you have a bigger distance to view the poster it might be lower.
This sounds like a class assignment...
I'm suspecting the expectation here is you will be submitting an exported PDF from InDesign. There is a Press Quality PDF preset, though out here in the real world it's a bit out of date, with the current recommendation being to use the PDF/X-4 preset for any printer who can handle the color conversions in a color managed workflow. PDF/X-4 preserves the colors in your document and tags them all with their color profiles for conversion downstream. Press Quality converts everything to CMYK and does not embed any profiles, so it is vital that you know the correct profile for conversion before you export.