$12x^{3}y\ast (-6x^2)\ast 0,5x{y}^2=(12\ast (-6)\ast 0,5)\ast x^{3+2+1}{y}^{1+2}=-36x^6{y}^3$
k = −36

$0,4p^4{q}^7:(-3\frac{3}{5}{p}^{3}q)\ast (-3p{q}^3{)}^2=0,4p^4{q}^7:(-\frac{18}{5}{p}^{3}q)\ast 9p^2{q}^6=\frac{2}{5}{p}^4{q}^7\ast (-\frac{5}{18p^{3}q})\ast 9p^2{q}^6=(\frac{2}{5}\ast (-\frac{5}{18})\ast 9)p^{4-3+2}{q}^{7-1+6}=(-\frac{1}{9})\ast 9)p^3{q}^{12}=-p^3{q}^{12}$
k = −1

$\frac{1}{7}m{n}^5\ast 4m^{3}n\ast 1\frac{3}{4}{m}^2=\frac{1}{7}m{n}^5\ast 4m^{3}n\ast \frac{7}{4}{m}^2=(\frac{1}{7}\ast 4\ast \frac{7}{4})m^{1+3+2}{n}^{5+1}=m^6{n}^6$
k = 1

$-3a^5{b}^3\ast 2a{b}^4:(-2a^{2}b{)}^3=(-3\ast 2)a^{5+1}{b}^{3+4}:(-8a^6{b}^3)=-6a^6{b}^7\ast (-\frac{1}{8a^6{b}^3})=\frac{6}{8}{a}^{6-6}{b}^{7-3}=\frac{3}{4}{a}^0{b}^4=\frac{3}{4}{b}^4$
$k=\frac{3}{4}$