Mail a letter to Vienna, Austria the post office charges a flat rate of $8.00 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+8.00, where y is the cost of the postage and x is the weight of the letter in ounces. i have to estimate to the nearest quarter of a dollar sing a graph. (0.25) the cost of the letter is is 3 ounces.