To combine the expressions \( (13x + 9y) + (38x + 33y) \), you can simply add the coefficients of like terms together.
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Combine the \(x\) terms: \[ 13x + 38x = 51x \]
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Combine the \(y\) terms: \[ 9y + 33y = 42y \]
Putting it all together, you get: \[ 51x + 42y \]
So, the simplified expression is \( \boxed{51x + 42y} \).