How many quarts of pure antifreeze must be added to 6 quarts of a 10% antifreeze solution to obtain a 60% antifreeze solution?

x+0.1(6) = 0.3(x+6) Simplify and solve for x.
x+0.6 = 0.3x+1.8 Subtract 0.3x from both sides.
0.7x+0.6 = 1.8 Subtract 0.6 from both sides.
0.7x = 1.2 Finally, divide both sides by 0.7
x = 1.71429
So you'll need to add 1.71429 quarts of pure antifreeze to the 6 quarts of 10% antifreeze solution to obtain 7.71429 (6+1.71429) quarts of 30% antifreze solution.