Bogdanov I.I.

Papa Carlo has 130 planks. From 5 planks, he can make a toy windmill, from 7 planks - a steamboat, and from 14 planks - an airplane. An airplane costs 19 gold, a steamboat - 8 gold, and a windmill - 6 gold. What is the maximum amount of gold Papa Carlo can earn?
For one airplane, the same 14 planks are required as for two steamships, but the airplane generates more revenue. Therefore, it makes no sense to build more than one steamship. From 15 planks, you can build three mills (revenue of 18 gold) or an airplane (revenue of 19 gold, and the extra plank won't hurt). Therefore, it makes sense to build no more than two mills. This means that for steamships and mills, Papa Carlo should use no more than $7+2 \cdot 5=17$ planks. Therefore, he should build 8 or 9 airplanes.

In the second case, we will get only 9 airplanes, and in the first case, in addition to 8 airplanes, the planks will be enough for two mills and a steamship (which is more expensive than an airplane).

In total, Papa Carlo will earn $8 \cdot 19+2 \cdot 6+8=172$ gold.

## Answer

172 gold.