Solve the following LP using the revised simplex method. Employ the Big M method to find an initial basic feasible solution.

$0,5x_3,+x_{4}20$

$x_1,x_2,x_3,x_{4}0$

$2x_1,+x_2,-x_3,+3x_4,60$

$0,5x_1,-1,5x_2,+0,5x_3,+x_4,30$

$x_1,+3x_3,+2x_4,=50$

$0,5x_3,+x_4,20$

$x_1,x_2,x_3,x_{4}0$