The following figures are parallelogram. find X and y​

Explanation:

For any parallelogram, the diagonals always cut each other in half.

This means the pieces that are y+5 and 18 cm long are equal

y+5 = 18

y = 18-5

y = 13

And so are the pieces that are x+y and 16 cm long

x+y = 16

x+13 = 16

x = 16-13

x = 3

Side note: the term "bisecting" is often used when saying "cutting in half".