If you want to find a better teacher for high school students, you should be prepared to spend more money. Experienced teachers like 1 (non-college students) 1 hour are the lowest, and the better, the more expensive. Of course, college students don't have to pay 1, so it's cheaper, and the awesome people in good universities may charge 100.
I hope it helps you.
For the flow of each line segment, establish a limiting formula, such as:
S _ a & lt= 26
S _ b & lt= 12