Problem Solving (PS) | Re: The sides of rectangle X are each multiplied by a to form re

Let rectangle X length=l width=w => Area = l*w
So now: rectangle Y length=a*l width=a*w => Area =a^2* l*w
rectangle Z length=b*l width=b*w => Area =b^2* l*w

given: a* Area of X = 10 = a*l*w
b* Area of X = 5 = b*l*w

so we can write a*l*w+b*l*w=10+5
=> l*w(a+b)=15

Also given => Area of Y - area of Z = 300 = a^2*l*w -b^2*l*w

so lw(a^2-b^2)=300
=> l*w(a+b)(a-b)=300
=> 15 (a-b)=300
=> (a-b)= 20


Answer: B

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