72/(1.5x)+72/x =1x =120 days, 1.5X= 180 days to solve the equation, that is, it takes team A 180 days to complete the project alone.

(2) The total cost of the project completed by Team A alone is 0.8x10000x180+100x =1458000 yuan.

Now team B is required to construct alone, and the total construction cost cannot exceed that of team A. Assuming that the average construction cost of team B alone is Y yuan, then

120y+120x100 ≤1458000 When solving the inequality, Y≤ 12050 (yuan), that is, only the daily average cost of construction team B is at most 12050.