>>Working together, Linda and Kathy can clean a beach house in 5.14 hours.<<
So, their rate working together is 1 house per 5.14 hours or
or 
>>Had she done it alone it would have taken Linda 11 hours.<<
So, Linda's rate working alone is 1 house per 11 hours or
or 
>>How long would it take Kathy to do it alone?<<
Suppose it would take Kathy x hours to do it alone.
So, Kathy's rate working alone is 1 house per x hours or
or 
The equation comes from:
+
=
Eliminate the decimal by multiplying top and bottom of the last fraction
by 100
+
=
Multiply through by 5654x
514x + 5654 = 1100x
5654 = 586x
= x
= x
9.648464164 = x
Round off to hundredths 9.65 hours.
Edwin