请用视频讲解这道题---**Question Stem:**
5. 某旅客携带 x(单位: kg) 的行李乘飞机, 登机前, 旅客可选择托运或快递行李, 托运费 y1(单位: 元) 与行李重量 x(单位: kg) 的对应关系由如图所示的一次函数图像确定. 下表列出了快递费 y2(单位: 元) 与行李重量 x(单位: kg) 的对应关系.
**Chart Description:**
Type: Line chart representing a linear function.
X-axis: Labeled "行李的重量 x/kg" (Luggage Weight x/kg). Values marked are 0, 30, 50.
Y-axis: Labeled "y1/元" (y1/yuan). Values marked are 0, 300, 900.
Line: A straight line starts from the origin (0, 0) and passes through (30, 300) and (50, 900). Dotted lines are shown from x=30 up to the line and across to y=300, and from x=50 up to the line and across to y=900. The line represents the relationship between check-in fee y1 and luggage weight x.
**Table: Express Delivery Fee y2**
| 行李的重量 x/kg (Luggage Weight x/kg) | 快递费 (Express Fee) |
| :--------------------------------------------- | :------------------- |
| 不超过 1 kg (Not exceeding 1 kg) | 10 元 (10 yuan) |
| 超过 1 kg 但不超过 5 kg 的部分 (Portion > 1 kg ≤ 5 kg) | 3 元/kg (3 yuan/kg) |
| 超过 5 kg 但不超过 15 kg 的部分 (Portion > 5 kg ≤ 15 kg) | 5 元/kg (5 yuan/kg) |
**Sub-questions:**
(1) 如果旅客选择托运, 求可携带的免费行李的最大重量为多少千克?
(If the passenger chooses to check in, what is the maximum weight of free luggage allowed in kilograms?)
(2) 如果旅客选择快递, 当 1 < x ≤ 15 时, 直接写出 y2 与 x 之间的函数关系式;
(If the passenger chooses express delivery, when 1 < x ≤ 15, directly write the functional relationship between y2 and x;)
(3) 某旅客携带 25 kg 的行李, 设托运 m kg 行李 (10 ≤ m < 24, m 为正整数), 剩下的行李选择快递. 当 m 为何值时, 总费用 y 的值最小? 并求出其最小值是多少元?
(A passenger carries 25 kg of luggage. Suppose m kg of luggage is checked in (10 ≤ m < 24, m is a positive integer), and the remaining luggage is sent by express delivery. What is the value of m when the total cost y is minimized? And what is the minimum value in yuan?)