$($a$)$ Assume that the given objective function: $J(x)=-2x_1{x}_2+2x_2+4x_3-2x_1{x}_3{x}_4+6x_4+$

$3x_1-2x_1{x}_2{x}_3{x}_4.$ If we apply Sequential forward feature Selection to completion, what will be

the optimal feature subset?

$($b$)$ Compare and contrast filter and wrapper feature selection methods.

$(2$ marks$)$