Question 432501
The initial amount of baking soda in the 40% solution = 0.40*180 = 72 liters
Let x = the number of liters of baking soda to add
For a 70% solution we have
0.70 = (72+x)/(180+x) 
since the same amount, x, is added to the solution and the original amount of baking soda
Solve for x:
0.7(180+x) = 72+x
126 + 0.7x = 72 + x -> 0.3x = 72 -> x = 180 liters
Check:
(72+180)/(180+180) = 252/360 = 0.7