[Question]: Amanda needs 12 more marbles to have twice as many marbles as Katrina, and Mabel has 5 times as many marbles as Katrina. If Mabel has 85 marbles, how many more marbles does Mabel have than Amanda?
[Answer]: Katrina has 85 / 5 = 17 marbles. Twice as many marbles as Katrina is 17 x 2 = 34. Amanda has 34 - 12 = 22 marbles. Mabel has 85 - 22 = 63 more marbles than Amanda.
So the answer is 63.

[Question]: James has 28 marbles. He puts them into 4 bags. He puts the same number in each bag. He then gives one bag away. How many marbles does James have left?
[Answer]: James has 28 marbles / 4 bags = 7 marbles per bag. James has 28 marbles - 7 marbles = 21 marbles remaining.
So the answer is 21.

[Question]: There are 20 sandcastles on Mark's beach, each with 10 towers. On Jeff's beach, there are three times as many castles as on Mark's beach, each with 5 towers. What is the combined total number of sandcastles and towers on Mark's and Jeff's beaches?
[Answer]:
The total number of towers at Mark's beach is 20 * 10 = 200 towers. There are 200 + 20 = 220 sandcastles and towers on Mark's beach. Jeff's beach has 3 * 20 = 60 sandcastles, three times as many as the number of sandcastles in Mark's beach. The number of towers in each of the sandcastles on Jeff's beach is 1 / 2 * 10 = 5. Since each sandcastle has 5 towers on Jeff's beach, there are 5 * 60 = 300 towers. In total, on Jeff's beach, there are 300 + 60 = 360 towers and sandcastles. Altogether, 360 + 220 = 580 sandcastles and towers can be found on their beaches.
So the answer is 580.