You can set up an equation to solve it. Suppose that X kilograms of water and Y spoons of washing powder need to be added to the washing machine, and then it can be obtained according to the known equations x+0.02*y+4.94= 15, 0.02*y/ 15=0.4%.
3. First, consider that m and n are known quantities. Since both X and Y satisfy the equation, it holds true for any equation, and so does x-y= 1 and x+y=3. Substitute the calculated x=2, y= 1 into equation 2-m=2n, 2n- 1 =.