Answer:
21 days
Explanation:
This is an inverse proportion, since the number of days required will be less the more people there are.
let number of people be p and days be d, then the equation is
d =
← k is the constant of proportionality
to find k use the condition d = 28 when p = 9, hence
k = dp = 28 × 9 = 252
hence d =
![(252)/(p)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/aibhz8ji1nhpwkec5r8xrpkp18kxpdvl2a.png)
when p = 12, then
d =
= 21 days