Question 1088646
Let x: ml. of the 4% solution
    y: ml. of the 1% solution

x+y = 1,800 (total solution)
0.04x +0.01y = 0,02(1,800) = 36 (total component)

Solving x=600 ml. and y= 1,200 ml.

So answer is we need 600 ml of the 4% and 1,200 ml of the 1% solution.

In a more general case, we need 1/3 of the 4% solution and 2/3 of the 1% solution to make a solution of 2%.

4%x/3+ 1%*2x/3 = 2%*x when x is the total  ml. of the solution.

@natolino_