To mail a letter to Vienna, Austria the post office charges a flat rate of $7.50 and an additional $0.50 for every ounce the letter weighs. The cost of mailing a letter is determined by the equation y=0.50x+7.50, where y is the cost of the postage and x is the weight of the letter in ounces. Step 1 of 2 : Graph the equation by finding two points that satisfy the equation and plotting them on the graph. To plot a point, click on the appropriate position on the graph. You may move a point by clicking and dragging.