Let s be the number of cheerleaders who need a size 6 and t be the number who need a size 12. We know that s = 2t and s + t + 4 = 19.
Substituting the first equation into the second equation, we get 2t + t + 4 = 19
Combining like terms, we get 3t + 4 = 19
Subtracting 4 from both sides, we get 3t = 15
Dividing both sides by 3, we get t = 5
Substituting that value back into the equation s = 2t, we get s = 2 * 5 = <<2*5=10>>10
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