We can use distribution property to multiply the polynomial by the monomial.
$$ \begin{aligned} \left( -3x+3 \right) \cdot \left( \color{orangered}{-x} \right) &= \left( -3x\right) \cdot \color{orangered}{-x} + 3 \cdot \color{orangered}{-x} = \\ &= 3x^2-3x \end{aligned} $$