I understand that you matrix equation to be solved to get LHS provided you have the variables 
.
. Here is a code which can be used to solve:
x_1 = 2;
x_2 = 3; %you can change these variables of LHS accordingly
x_3 = 4;
u = 5;
x = [x_1; x_2; x_3]; %generate a column matrix
A = [-42.3729 0 0; 0 0 1; -0.7670 -0.0012 0]; % generate the 3 X 3 matrix as given in equation
B = [1.6949; 0; 0]; %generate the 3 X 1 matrix as given in equation
X = A * x + B * u %X matrix is the x dot matrix of the equation
