Therefore, 250 = 200 + C
or
C = 50
Then (2) reduces to
y = 200 + 50 
40
t
e
− (3)
or
200
50
y−
 = 
40
t
e
−
or
40
t
e
 = 
50
200
y−
Therefore
t = 40
50
200
loge
y −
 (4)
Here, the equation (4) gives the time t at which the salt in tank is y kg Step 4 Since 
40
t
e
−
 is always positive, from (3), we conclude that y > 200 at all times
Thus, the minimum amount of salt content in the tank is 200 kg