Sederhanakanlah. (1) 1/2 x + y - (2/3 x - y/2) (2) x - y -

Sederhanakanlah. (1) 1/2 x + y - (2/3 x - y/2) (2) x - y - (3x - y)/4 (3) 3a^2 : 6ab x (-2a)^2 (4) 9x^2 x (-xy) : 3/5 y^3