Question 72161
This is a comboned rate problem
The rate with their own hose is:
 one pool filled / 12 hrs
The comboined rate is:
one pool filled / 7 hrs
The rate with the neighbor's hose is
one pool filled / x hrs
The equation is
{{{1/12 + 1/x = 1/7}}}
multiply both sides by 12*7*x
{{{7x +  12*7 = 12x}}}
{{{5x = 84}}}
{{{x = 16.8}}}hrs with neighbors hose