Hello, please take a look at the work below:
Original Enclosure: Length is 15, Width is 10. So, the Area is length x width, giving you 15 m x 10 m = 150 m^2.
What would be your new area for the larger enclosure? Well, 150 x 2 = 300 (do this because you want to double the enclosure's area.
Okay, so we have established that the new area needs to be 300 m^s. Now let's look at the new length and width.
Let us set x as the amount that both the length and width are increased by (since they are increased by the same amount, x works for both).
So we have:
Length = (x+15) <---------- 15 for the original length, added to x (to be determined)
Width = (x+10) <----------- 10 for the original width, added to x (to to determined)
So, New Area = New Length x New Width
300 = (x+15)(x+10)
300 = x^2 +10x +15x +150 <------------- FOIL
300 = x^2 +25x +150
0 = x^2 +25x - 150 <-------------- subtract 300 from each side
0 = (x + 30) (x - 5) <-------------- Factor
Set x+30 = 0 and x-5 = 0
x = -30 or x = 5..... can length be negative? No. So -30 is not possible. We must choose x=5.
New length: 5 + 15 = 20 m
New width: 5+ 10 = 15 m
Check: 15 x 20 = 300 and we are good to go!
As for the diagrams, you should draw a rectangle with length as 15 and width 10, and then a new one with length = (x+15) and width = (x+10)