Achemist wants to make 50ml of a 16% acid solution by mixing a 13% acid solution and an 18% acid solution. how many milliliters of each solution should the chemist use?

X=amount of 13% acid solution
50-x=amount of 18% acid solution (cuz they add up to 50 mL)
to find the number of millimeters of solution needed, find their acid concentrations and use those to find the volume of solution:
x*0.13 + (50-x)*0.18 = 50*0.16
expand and simplify:
0.13x-0.18x+9=8
-0.05x+9=8
-0.05x=-1
0.05x=1
x=20 mL of 13% solution
50-x=30 mL of 18% solution