The water fee in the second quarter is 1.25 times that in the first quarter, that is,1.25x =1.25 (a+40)/3, that is, (5a+200)/ 12 yuan.
In the second quarter, 75%(2x-40)=0.75(2a-40)/3, namely (a-20)/2 yuan.
(2) In the first quarter, the water fee is still set to X, with
(x+2x-40)-[ 1.25 x+0.75(2x-40)]= 4 10
The solution is x= 1680 yuan.
28.