a) `3(2x - 1) - 5(4x - 2)`
`= 6x - 3 - 20x + 10`
`= -14x + 7`
c) `(-3x² + $\frac{2}{3}$xy - y²)(-$\frac{1}{2}$xy)`
`= -(3x² - $\frac{2}{3}$xy + y²) × -($\frac{1}{2}$xy)`
`= (3x² - $\frac{2}{3}$xy + y²)($\frac{1}{2}$xy)`
`= $\frac{3}{2}$x³y - $\frac{1}{3}$x²y² + $\frac{1}{2}$xy³`