In order to calculate the area of the rhombus, first let's draw the diagonal BD.
This diagonal and the diagonal AC will intersect at point M, which is the midpoint of each diagonal.
Since M is midpoint of AC, we have AM = MC = 7 cm.
Now, let's calculate the length of BM, using the Pythagorean theorem in the right triangle BMC:
Calculating the area of this triangle, we have:
The triangles BMC, BMA, DMC and DMA are all congruent, so the area of the rhombus is: