The ratio of side lengths of similar figures is the same as the ratio of any linear measure on those figures, including perimeter. The second figure's perimeter is 10/16 of that of the first figure, so the shortest side of the second figure will also be 10/16 of the length of the shortest side of the first figure.
(10/16)×(4 cm) = 2.5 cm
The shortest side of the second polygon has a length of 2.5 cm.
