I can't figure out this word problem, can ya help for them points

A 12-qt cooling system is checked and found to be filled with 25% antifreeze. The desired strength is 50% antifreeze. How many quarts need to be drained and replaced with pure antifreeze to reach the desired strength?

12 * 25%+100%(pure antifreeze) *x= 50% * (12+x)
300+100x= 600 + 50x
you get 6 quartz :)

3qt