Let's take a look at what's going on:
Original parking lot:
Therefore, the original area of the parking lot would be
[tex]50\cdot40=2000[/tex]Increasing x yards in each side:
The area of this rectangle would be:
[tex](50+x)(40+x)[/tex]And we know that the school wants it to be 1000 square yards greater than the original area (2000). The new area would have to be 3000
Thus,
[tex](50+x)(40+x)=3000[/tex]