Step 1: Understand the question and note down the known values

Step 2: Make an equations for the given information.

            NOTE: Write the equivalent term of the arithmetic sequence and equate

             to  the given term to form an equation.

             Write the sum of the n terms formula  and equate it with the    

            appropriate values  

           EXAMPLE: The longest side of the polygon has length 6 cm

                                 a + 15d = 6

                              The perimeter of the polygon is 72 cm

                                n/2 [2a + (n − 1)d] = 8 (2a + 15d) = 72 (since n = 16) 

Step 3:  Solve these equations(linear equations) to find the unknown values

Step 4: In this question shorter length is the starting side. So first side is nothing but a value of  "a".