Question 720881
The amount of sodium hydroxide in the new solution will be 5% of 10 liters plus 8% of 5 liters.  The amount of new solution is predictably near 10+5 liters.  The result wanted in amount of pure sodium hydroxide divided by amount of the resulting solution, multiplied by 100 in case decimal fractions were used.  The concentration would be assumed % weight per volume.