Tìm x

a) 3/7x - 2/3x = 10/21
b) 7/35 : ( x - 1/3 ) = -2/25
c) 3 ( x - 1/2 ) - 5 ( x + 3/5 ) = - x + 1/5
d) ( 2x - 1 ) ( x + 2/3 ) = 0