Let the two sides that are equal in length have length x.

So the three sides have lengths x,x,x+20 centimeters.

perimeter = (x)+(x)+(x+20) = 3x+20 ≧ 95
                                3x ≧ 75
                                 x ≧ 25 cm

The triangle inequality says the sum of two sides with minimal
lengths is strictly greater than the third side:

x+x > x+20   
 2x > x+20
  x > 20 cm

That requirement is fulfilled by x ≧ 25

The two sides that are equal in length have length x ≧ 25 cm.
The third side is exactly 20 cm more than x.  So it must be
45 cm or longer.

Edwin