Welcome to the site !!
What I would do is get the sprocket combo you want to use and install them , center out the axle adjusters so you have equal distance going each direction , then take your current chain and wrap it around (use a old shoelace thru the link holes to hold it in place snugly , so the chain is where it would be when connected/adjusted) , then measure the physical distance missing , then remove the chain and lay it out flat , then put the tape on your chain , and count the number of links in that measurement you just did , this will give you the amount of links needed without racking your brain trying to calculate it ... simple and easy , as there are too many variables because of the amount of adjustment can add or subtract link count , you can be off 1-3 links because of where the adjusters are , and if your chain is stretched it adds another factor , so if you just measure the length of the missing links gap (count only the actual links , not in between links) and measure your chain and count the links in that measured space and you have the link count close enough to make any adjustments needed to compensate for discrepancies ...... That is what I would do .... mainly because I suck at math ...