To simplify the expression \((5y - 1) + (-2y + 4)\), we can start by removing the parentheses:
\[ 5y - 1 - 2y + 4 \]
Next, we will combine the like terms. The like terms here are the \(y\) terms and the constant terms:
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Combine the \(y\) terms: \[ 5y - 2y = 3y \]
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Combine the constant terms: \[ -1 + 4 = 3 \]
Putting it all together, we get:
\[ 3y + 3 \]
Thus, the simplified expression is:
\[ \boxed{3y + 3} \]