Question 230874
Hello, 

Let the two sides that are equal to each other be represented by x
The third side will be written as 1.5x - 3. 

These sides add up to 28.5 Cm
So an equation can be written as: 
 
                              x + x + 1.5x -3 = 28.5 cm

Combine like terms: 

                                     3.5x - 3 = 28.5

Add 3 to both sides:

                                         3.5x = 31.5

Divide each side by 3.5:

                                             x = 9

Therefore the lengths of the sides are   9 cm, 9 cm and 10.5 cm

RJ Toftness
Author of "Unlock the Mystery to Math" 
www.math-unlock.com