4. (7 points) Team A and Team B work together to dig a water channel that is 8250 meters long. Team B digs 150 meters more per day than Team A. If it is known that Team A worked alone for 4 days first, and then the remaining part was dug by both teams together for 7 days to complete the task, how many meters does Team A dig per day?

保留源文本的换行和格式，直接输出翻译结果如下：

4. (7 points) Team A and Team B work together to dig a water channel that is 8250 meters long. Team B digs 150 meters more per day than Team A. If it is known that Team A worked alone for 4 days first, and then the remaining part was dug by both teams together for 7 days to complete the task. That is, how many meters does Team A dig per day.
【Solution】Solution one: According to the problem, we know: Total work $=$ Jia works for 11 days + Yi works alone for 7 days $=$ Jia works for 11 days + (Jia works for 7 days $+150 \times 7$ )

So $(8250-150 \times 7) \div(11+7)=7200 \div 18=400$ (meters).
Solution two: Let Jia team dig $x$ meters per day, then Yi team digs $150+x$ meters per day. According to the problem, we can get the equation:
$$
\begin{aligned}
4 x+(x+x+150) \times 7 & =8250, \\
18 x+1050 & =8250, \\
18 x & =7200, \\
x & =400,
\end{aligned}
$$

Answer: Jia team digs 400 meters per day.
Therefore, the answer is: 400.