Find the value of "a" for which v=[-6 a -7 -8]is in the setH= span([-3 -5 -3 1][0 -3 -3 5][0 0 -4 -5]) looks like this

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Where those are column vectors that form a 4x3 matrix.I took the determinant of the system to solve for what a can't be but that wasn't right. Thanks for the help.

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I took the determinant of the transpose of the matrix and got a=13 which still isn't right.Also,Let P^R be the vector space consisting of all polynomials of degree R or less with real coefficients.Which of the following subsets of P^R are subspaces of P^R?a. p'(t)=9b. p(-t)=p(t) for all tc. p'(t) is a constant polynomiald. integral of p(t) dt from 0 to 6 = 0e. p(4)=1f. p(5)=0g. p'(t)+7p(t)+3=0I am not sure what it is asking for here.

0 -3 -5 0 0 -3 -3 -3 -4 15 -5