A plot of land is a square and its sides are x metres. It gets expanded so that the plot of 40 metres longer and 50 metres wider and so that it is 200 metres short of being double the area of its original size. What is x?

I have got as far as working out:

Original Perimeter is 4x

Original Area is 2x

New perimeter is 4x + 180

New Area = 4r - 200 = 2r - 100

I am unsure where to take it from here though. Help would be appreciated.