Acontractor crew can frame 3 houses in a week how long will it take them to frame 54 houses if they frame the same number each week

To set up an equation for this you can use a variable to represent your unknown (in this case the unknown is how long it will take to frame 54 houses)

We know that 3 houses can be framed in 1 week so you can represent the equation as 

3x=54 (3 being the amount of houses framed in 1 week, x being how many weeks it will take to frame 54 houses)

You can isolate X by dividing both sides by 3 (3x/3 = 54/3) which simplifies to 
x = 54/3