To simplify the expression \((18x + 9y) + (2x + 6y)\), we first combine like terms.
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Combine the \(x\) terms:
- \(18x + 2x = 20x\)
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Combine the \(y\) terms:
- \(9y + 6y = 15y\)
Putting it all together, we get: \[ 20x + 15y \]
So, when simplified, the expression is \(20x + 15y\).
Thus, the coefficients are:
- For \(x\), the coefficient is 20.
- For \(y\), the coefficient is 15.
Final answer: \[ 20x + 15y \]