Well, the average is easy, at least if all you want is a linear trendline. Just select a linear trendline for the expression. The max is more complicated. You only have one data point, so you technically can't make a line, but I'm guessing you want the line to go through (0,0). That makes the formula for your line just max(total "Margin %") * Sales. However, your linear trend line for the average doesn't necessarily go through (0,0). If you want it to be consistent with your max line, you might want to use Sales * sum(total Margin)/sum(total Sales).
What I don't know how to do is to set the bubble size to the Margin %. However, this is already roughly indicated by the position of the bubble. If it's above the average line, it's higher than average. If it's below the average line, it's lower than average. It doesn't seem like you'd need a second indicator of good margins.
If you really, really do, you could probably overlay a line chart on a scatter chart. A simple scatter chart allows for the linear trend line, but I don't think allows you to put in additional lines except for vertical or horizontal reference lines.
