The area of a parallelogram is 216 cm². The height of the parallelogram is 2/3 of its base. Find the base and height.

2 equations, 2 unknowns. Call height H and base B.

From the first sentence:

HB = 216

From the second sentence:

H = ⅔ B

Plug the second into the first and solve for B:

(⅔ B) B = 216

B^2 = 324

B = 18

Plug that back into either of the original 2 equations and solve for H:

H (18) = 216

H = 12