Question 252193
This question is a bit tricky in that they give you water and antifreeze. Just focus on the antifreeze numbers. Here is the table. "BIG SPACE" will mean leave a big space between the information in the columns. Your basic idea is correct, but I generally try to get one variable.

        %      BIG SPACE                   L      BIG SPACE                   %L
A     100  BIG SPACE                  X       BIG SPACE                 100X
B     50    BIG SPACE                 10-X  BIG SPACE                  500 - 50X
MIX 60    BIG SPACE                10       BIG SPACE                 600.

From this table, we have one formula:

100X + 500 - 50X = 600. Solving for X, we get X = 2.

You need 2Q of pure antifreeze and 8 Q of the 50% antifreeze.