7x + 3y - (-3х+ 3y):

To simplify the expression \(7x + 3y - (-3x + 3y)\), follow these steps:

1. Distribute the negative sign across the terms inside the parentheses: \[ -(-3x + 3y) = 3x - 3y \]

2. Now, substitute this back into the original expression: \[ 7x + 3y + 3x - 3y \]

3. Combine like terms:

   • Combine the \(x\) terms: \(7x + 3x = 10x\)
   • Combine the \(y\) terms: \(3y - 3y = 0\)

4. Thus, the simplified expression is: \[ 10x \]

So, \(7x + 3y - (-3x + 3y) = 10x\).