We know that the perimeter of the smaller parallelogram is 12 cm (2*2 + 4*2). Even though they are similar, this does not make the equation 4*2 + 6*2. Instead, try using the equation for missing side lengths: x/2 = 6/4. To make them similar, the value of x is 3. Plug this into the perimeter formula (3*2 + 6*2) and your answer is 18 cm.
