Ar = (c1%xA1+c2%xA2+c3%xA3)/100
238 = (238c1 + 235c2 + 234x0,006)/100
=> 23798,596 = 238c1 + 235c2
100 - 0,006 = c1 + c2 => c1 + c2 = 99,994
=> c2 = 99,994 - c1
=> 23798,596 = 238c1 + 235(99,994- c1)
=> c1 = 299,77/3 = 99,24%
=> c2 = 99,994 - 99,24 = 0,75%