Question 635208
Let x=time it takes Jacqueline to do the job alone
So Jacqueline works at the rate of 1/x of the job per hour
Then x-15 =time it takes Chase to do the job alone
And Chase works at the rate of 1/(x-15) of the job per hour
Together they work at the rate of 1/x + 1/(x-15) of the job per hour
But we are told that they can do the job, working together, in 4 hours
So together they work at the rate of 1/4 of the job per hour
Then our equation to solve is:
1/x + 1/(x-15)=1/4 multiply each term by 4x(x-15)
4(x-15)+4x=x(x-15) simplify
4x-60+4x=x^2-15x  collect like terms
x^2-23x+60=0  quadratic in standard form and it can be factored
(x-20)(x-3)=0
x=20 hours---Time it takes Jacqueline to do the job working alone
x-15=20-15=5 hours-----Time it takes Chase to do the job working alone
and 
x=3 hours----  IMPOSSIBLE ANSWER---WHY????
CK
1/20+1/5=1/4
1/20+4/20=1/4
5/20=1/4
1/4=1/4

Hope this helps----ptaylor