Question 200990
Rate  of  Sally = 1 house / 4 hrs  = .25 House / hr
.
Rate  of  John  =  1 house / 6 hrs = .167 house / hr
.
combined  rate  is  .417 house  per  hr,,,,(.25 +.167)
.
Rate  * Time  = Distance
.
.417  house / hr * t hrs = 1  house
.
t= 1 / .417 = 2.4 hrs
.
check
.
2.4 * 1/4 + 2.4 * 1/6 = .6+.4 =1,,,,,, ok