Let a Subscript $1$equalsleft bracket Start $3$ By $1$ Matrix $1$st Row $1$st Column $12$nd Row $1$st Column $23$rd Row $1$st Column negative $1$ EndMatrix right bracket

$,$ a Subscript $2$equalsleft bracket Start $3$ By $1$ Matrix $1$st Row $1$st Column negative $62$nd Row $1$st Column negative $53$rd Row $1$st Column $3$ EndMatrix right bracket

$,$ and bequalsleft bracket Start $3$ By $1$ Matrix $1$st Row $1$st Column $42$nd Row $1$st Column negative $203$rd Row $1$st Column h EndMatrix right bracket

$.$ For what$$ value$($s$)$ of h is b in the plane spanned by a Subscript $1$ and a Subscript $2?$