Question 1187579
Solving first for {{{A * B}}}, let {{{D = A * B}}},

{{{matrix(3,3,
i,j,k,
3,2,0,
2,3,1)}}}={{{i(2-0)-j(3-0)+k(9-4)=2i-3j-5k}}}

Let{{{ E=C*D}}}, then{{{ D[x]C[x]+D[y]C[y]+D[z]C[z]=2(5)+(-3)(0)+5(2)=20}}}