Let's call the amount of wins the Miami Dolphins had as "D", and the amount of wins the Kansas City Chiefs had as "K". From the sentence "the Miami dolphins won five times as many games as the Kansas city chiefs. " we know that D is five times bigger than K.
And from the sentence "Together, they won twelve games." we know that the sum of those two variables is 12.
Making a substitution, we can rewrite the D in the second equation as 5K.
Using our K value, we can substitute in any of our equations to get D.
The Miami Dolphins won 10 times, and the Kansas City Chiefs won 2 times.