Let x be the quantity in pounds of tea which he will be selling and which costs $7.8/lb Let y be the quantity in pounds of tea which he will be sellling and which costs $4.3/lb Then according to the problem, he wants to sell 50 lbs of tea at $5.14/lb. ie. 7.8x+4.3y=50*5.14...............(1) Since he wants to sell 50 lbs in total, x+y=50.......................(2) Now solve equns (1) and (2) simulatenously for x and y.