To find the missing length, we need to know the formula for the area of a rectangle, which is given by:
Area = length x width
Given that the area is 30 cm² and one side is 5 cm, we can rearrange the formula to solve for the missing length:
30 cm² = 5 cm x z cm
z cm = 30 cm² / 5 cm
z cm = 6 cm
Therefore, the missing length is 6 cm.