In 4 hours Bethany did the whole fraction 1 of the house.
In 1 hour he would do 1/4 of it.
In 3 hours Colin did the whole fraction 1 of the house.
In 1 hour he would do 1/3 of it.
In 1 hour they would both do (1/4 + 1/3)
If it takes both of them x hours to finish 1 whole fraction of the house.
In 1 hour they will both do 1/x
That means that:
1/x = 1/4 + 1/3
That is the equation. x can be solved for.
