We will need to have two equations here, having x as the missing length. We know that the chairs are in the same amount on each occasion, so each equation should be equal to the other.
This sets up a problem of:
6x + 7 = 4x + 13
7 and 13 being the leftover chairs and 6 and 4 being the rows. Let’s solve for x.
x = 3
Knowing this, we plug in x for one of the equations
