Isosceles triangle is a triangle with 2 sides that are equal and one side that may be different in length to the other 2.
I would presume the legs refer to the 2 sides of the triangle which are equal to each other.
First, divide the sides into countable units:
Let x be a unit measure,
Let x = the base length (aka. the length that is different for the other 2 sides)
Since the base length is one fourth (I.e. 1/4) of one of the other (equal) sides, the other side will be 4x.
Since the 2 sides are the same length, the 3rd side will be 4x as well.
Add all 3 sides together, you'll get the perimeter, 4x + 4x + x = 25 <all in inches>
=> 9x = 25
=> x = 25/9
= 2 7/9 inches
Hope this helps!