Similar figures have the same size but not necessarily the same size.
The respective sides will be in the same ratio in a similar figure.
So from the information given you can't say what the measure of the perimeter of quadrilateral EFGH is. All you can say is the ratio of the perimeters is the same as the ratio of the respective sides. If the ratio is 1:2 for example then the perimeter of EFGH is 2*4y^2 = 8y^2.
