x quarts of pure antifreeze
6*0.3 = 1.8 quarts antifreeze in a 30 % antifreeze solution
(x+6) - We are going to get a 40 % antifreeze solution
0.4*(x+6) - quarts antifreeze in a 40 % antifreeze solution
x quarts of pure antifreeze + 1.8 quarts antifreeze in a 30 % antifreeze solution= = 0.4*(x+6) quarts antifreeze in a 40 % antifreeze solution,
so we can write an equation
x+ 1.8 = 0.4*(x+6)
x+1.8 = 0.4x +2.4
0.6x = 0.6
x=1 quart of pure antifreeze
