A rectangular pool is twice as long as the it is wide and has a 10 foot walkway surrounding it. If the border has an area of 2800 ft^2 find the perimeter of the pool

so the Length of the border will be 2x+20 and the width be x+10

I have figured out x=40 and the perimeter to equal 240ft? I set my equation to be x^2+10x=1400

Not sure it that is correct?