Question 824510
I did not see either your previous posting of the same problem, or the solution provided to you.
I could be saying the same thing all over again.
You would figure the rate at which each one works as
(work completed)/(time needed),
and you would figure out that rates add up,
because the rates mean how much work each one can do in an hour, and the amounts of work add up for each hour
(at least in math problems, where a worker can work as fast when starting work as when tired, after working for several hours).
The work rates for Cody and Kaitlin are known.
For Cody, the rate is
{{{1park/"8 hrs")=(1/8)}}}{{{parks/hour}}} .
For Kaitlin , the rate is
{{{1park/"6 hrs")=(1/6)}}}{{{parks/hour}}} 
It it takes Joseph {{{x}}} hours to do the whole park by himself,
his rate would be {{{1park/"x hrs")=(1/x)}}}{{{parks/hour}}} .
With the three of them working together, they may take {{{t}}} hours to do the park.
Their joint rate would be {{{(1/t)))){{{parks/hour}}} ,
and we can conclude that
{{{1/t=1/8+1/6+1/x}}}
I can work with that equation to express it in other forms,
but with the data you have provided,
all I can get is {{{x}}}} as a function of {{{t}}}.,
or {{{t}}}} as a function of {{{x}}} .
It stands to reason that {{{1/t>=1/8+1/6=(6+8)/48=14/48=7/24}}} ,
so {{{t<=24/7}}} .
Beyond that, I cannot do anything else.