You have to make a solution of NADH, a biochemical cofactor, with concentration 50 g/mL. Not using a scale, you dissolve a small amount of NADH in 1mL water and measure an absorbance at 340nm of 0.874. The molecular weight of NADH is 663.43g ans it's absorbance coefficient is 6220 M^-1 cm^-1. How much of your solution do you have to dilute to obtain the desired concentration not exceeding volume of 1mL?