13. There is a vegetable field and a wheat field. Half of the vegetable field and $1 / 3$ of the wheat field put together is 13 hectares. Half of the wheat field and $1 / 3$ of the vegetable field put together is 12 hectares. Then, how many hectares is the vegetable field?
13.【Solution】Three times the vegetable field and two times the wheat field is $13 \times 6$ hectares. Two times the vegetable field and three times the wheat field is $12 \times 6$ hectares,

Therefore, the total area of the vegetable field and the wheat field is: $(13 \times 6 + 12 \times 6) \div (3 + 2) = 30$ (hectares),

The vegetable field is $13 \times 6 - 30 \times 2 = 18$ (hectares).