Lisa is standing on a dock beside a lake. She drops a rock from her hand into the lake. After the rock hits the surface of the lake, the rock's distance from the lake's surface changes at a rate of −3 inches per second. If Lisa holds her hand 3 feet above the lake's surface, how far from Lisa's hand is the rock 3 seconds after it hits the surface.

  7.5 meters

Step-by-step explanation:

As with many quadrilaterals, pairs of sides have the same length, so the perimeter is twice the sum of two of the sides.

In a kite, generally, opposite sides have different lengths, so the perimeter is twice the sum of the lengths of opposite sides. That is

  51 m = 2(18m + side opposite)

  15 m = 2 × (side opposite)

  7.5 m = side opposite

Comment on side lengths

In a rectangle or parallelogram, the perimeter is twice the sum of adjacent sides. A kite is different in that adjacent sides may be the same length. If the kite is not a rhombus, opposite sides are always different lengths.