\(\dfrac{2}{5}-\dfrac{8}{9}\cdot\dfrac{-27}{40}\)

\(=\dfrac{2}{5}-\left(-\dfrac{216}{360}\right)\)

\(=\dfrac{2}{5}+\dfrac{216}{360}\)

\(=\dfrac{2}{5}+\dfrac{3}{5}\)

\(=\dfrac{5}{5}=1\)

\(2\sqrt{5}-3\sqrt{125}+\sqrt{52}-2\sqrt{8}\)

\(=2\sqrt{5}-15\sqrt{5}+2\sqrt{13}-4\sqrt{2}\)

\(=-13\sqrt{5}+2\sqrt{13}-4\sqrt{2}\)

\(\dfrac{1}{2}-\left(40\%-0,75\right)\)

\(=\dfrac{1}{2}-\left(\dfrac{40}{100}-\dfrac{3}{4}\right)\)

\(=\dfrac{1}{2}-\left(\dfrac{2}{5}-\dfrac{3}{4}\right)\)

\(=\dfrac{1}{2}-\left(\dfrac{8}{20}-\dfrac{15}{20}\right)\)

\(=\dfrac{1}{2}-\left(-\dfrac{7}{20}\right)\)

\(=\dfrac{1}{2}+\dfrac{7}{20}\)

\(=\dfrac{10}{20}+\dfrac{7}{20}\)

\(=\dfrac{17}{20}\)

\(3\left(x-1\right)+3=12\)

\(3\left(x-1\right)=12-3=9\)

\(x-1=9:3=3\)

\(x=3+1=4\)