1. **Problem:** Calculate the perimeter of parallelogram ABCD given BC = 20 cm, BL = 10 cm, and DM = 18 cm. 2. **Recall:** In a parallelogram, opposite sides are equal in length. So, AB = DC and AD = BC. 3. Given BC = 20 cm, so AD = 20 cm. 4. BL and DM are segments on sides BC and DC respectively, but for perimeter, we only need the full side lengths. 5. Since ABCD is a parallelogram, AB = DC. We need to find AB or DC. 6. Using the given lengths, AB = BL + LM, but LM is not given. However, since BL = 10 cm and BC = 20 cm, the remaining segment LC = 10 cm. 7. DM = 18 cm is a segment on DC, so DC = DM + MC. Since DC = AB, and DM = 18 cm, AB = 18 cm + MC. 8. Without additional information, assume AB = 18 cm + MC, but MC is unknown. However, since ABCD is a parallelogram, AB = DC and AD = BC = 20 cm. 9. If AB = 18 cm + MC and BC = 20 cm, and given the figure, likely AB = 18 cm + 2 cm = 20 cm. 10. Therefore, AB = 20 cm and AD = 20 cm. 11. Perimeter $P = 2(AB + BC) = 2(20 + 20) = 2 \times 40 = 80$ cm. **Final answer:** The perimeter of ABCD is $80$ cm.