[Question]: Johnny is buying planks of wood to build some tables. Each table needs a plank of wood for each of the legs and 5 planks of wood for the surface. If Johnny wants to build 5 tables, how many planks of wood does he need?
[Answer]: Each table needs 1 plank of wood * 4 legs = 4 planks of wood for the legs. This means each table needs 4 planks of wood for legs + 5 planks of wood for the surface = 9 planks of wood. To build 5 tables, Johnny will therefore need 9 planks of wood * 5 tables = 45 planks of wood.
So the answer is 45.

[Question]: Derek was 6 years old when he had three times as many dogs as cars. Ten years later, after selling some of his dogs and buying 210 more cars, the number of cars became twice the number of dogs. How many dogs does Derek have now if he had 90 dogs when he was six years old?
[Answer]: At six years old, with three times as many dogs as cars, Derek had 90 / 3 = 30 cars. Ten years later, after buying 210 more cars, Derek has 210 + 30 = 240 cars. Since the number of cars is twice as many as the number of dogs, Derek currently has 240 / 2 = 120 dogs.
So the answer is 120.

[Question]: A child is making a 5-level pyramid by stacking some blocks. In the first row, he has 9 blocks. For the next rows, he has 2 less than the blocks he has from its bottom row. How many blocks did he use in all?
[Answer]:
On the second row, he used 9 - 2 = 7 blocks. On the third row, he used 7 - 2 = 5 blocks. On the fourth row, he used 5 - 2 = 3 blocks. On the fifth row, he used 3 - 2 = 1 block. Therefore, he used a total of 9 + 7 + 5 + 3 + 1 = 25 blocks.
So the answer is 25.