Answer:
12 ft. more length of moat will be required.
Step-by-step explanation:
Initially, the sandcastle measured 19 ft by 11 ft and the length of the moat around it will be the perimeter of the castle.
So, initially, the moat was of 2(19 + 11) = 60 ft long.
Now, Mar decided to change the castle size as 12 ft by 24 ft.
Therefore, the length of the moat around it will be 2(12 + 24) = 72 ft. long.
Hence, (72 - 60) = 12 ft. more length of the moat will be required. (Answer)