用linq清理一个简单的foreach

The following method is pretty simple, I'm trying to determine a line-item rate by matching up another property of the line-item with a lookup from a parent object. There's a few things I don't like about it and am looking for elegant solutions to either make the method smaller, more efficient, or both. It works in it's current state and it's not like it's noticeably inefficient or anything. This isn't mission critical or anything, more of a curiosity. The following method is pretty simple, I'm tryi