( 7,8 - 3,2x ) * 5/6 = ( 1,2 - 4x ) : 8/15
( 39/5 - 16/5x ) * 5/6 = ( 6/5 - 4x ) : 8/15
13/2 - 8/3x = 9/4 - 15/2x
15/2x - 8/3x = 9/4 - 13/2
( 15x * 3 - 8x * 2 ) / 6 = 2,25 - 6,5
( 45x - 16x ) / 6 = - 4,25
29x = - 4,25 * 6
29x = - 25,5
x = - ( 51/2 ) : 29
x = - 51/58