Answer:
12 centimeters
Explanation:
The double dashes are both the same number. Since the base is 4cm and they have to be two of the same number, the double dashes are each 2cm long. Meanwhile, the height is 2cm, and the single dashes are two of the same numbers (but not 2cm, because that's what the double dashes are). So, each dash must be 1cm long. When you add them up:
