[tex]a) \ 10a - (6a+1)+7(6-a) = 10a - 6a - 1 + 42 - 7a = 41 - 3a\\\\\\b) \ 5(x+y)-9y-4(y-x)+x = 5x+5y-9y-4y+4x+x = 10x -8y\\\\\\c) \ 7-[4-(a+2)+6a]\cdot3 = 7-(4-a-2+6a)\cdot3 = 7-(2+5a)\cdot3=7-6-15a=\\\\=1-15a[/tex]
