Question 154169
Let x be the width, then the length is 3x.
So its area = length*width = 3x*x = 3x^2.
As the area is 75, we have
{{{3x^2=75}}}
Solving the quadratic equation, we have
{{{x^2=25}}}           (divide both sides by 3)
So 
{{{x=sqrt(25)=5}}} or {{{x=-sqrt(25)=-5}}}
As the width can not be negative, the solution x = -5 is rejected.
Thus the width is 5, and the length is 3x=3*5 = 15.