I believe it is A and Yes
The bigger the price is on an item, the more tax you would have to pay, so both numbers increase. As for whether or not there is a line through the dots, you use a line when you could go inbetween the points. For example, with this question you can have 0.24, 0.86, or any other number as the price and it would make sense. If the question was sales tax on a certain number of shirts, well, you can't buy half a shirt so you don't need anywhere inbetween the dots.
Proportional in these kinds of problems means whether or not the line curves. If it doesn't and is a straight line, then it is proportional.