Aplot of land doubles in size by adding x meters to the length and x meters to the width of the land. if the original plot had an area of 200 by 300 meters, what is the value of x?

Lets write as an equation the info provided in the problem:
original area = 200*300 = 60000 squared meters
Adding x meters to the length is: 300 + x
Adding x meters to the width is: 200 + x
If the area doubles in size we have: 2*60000
Now writing as a single equation all info:
(300 + x)(200 + x) = 120000
We have to make the operations and solve:
60000 + 300x + 200x + x^2 = 120000
x^2 + 500x - 60000 = 0
This is a squared trinomial, to solve it we need two numbers that subtracted give us 500 and multiplied -60000:
(x + 600)(x -100) = 0
So there are two solutions, x = -600 and x = 100, we choose the positive one:
x = 100
thererefore the value of x is 100 meters