why (6+10+4+4)/(6+10+4+4+1) X100% ?

you have found your domain, that is (4.52,16.28)

you need to find the percentage of weeks that fall within this domain. so just check which weeks in your data do fall in this domain. for example, 10 does, 8 does, 7 does, but not 4, not 18, then 9 does, 14 does, and so on... altogether there's 18 that fall in this domain. then 18/25 x 100% = 72%