[tex]12 x^{4} * (- \frac{5}{6} x^{3} y^{2}) [/tex]
Now multiple the coefficients and add the exponents with common bases
[tex]12 * - \frac{5}{6} = -10 \\ x^{4} + x^{3} = x^{7} [/tex]
Now write your final expression
[tex]-10 x^{7} y^{3} [/tex]
Hope I helped!