Need help with: Making a Matrix Singular and Finding Determinates

Ok, i have been working on these problems for a bout an hour now and cant seem to find an answer.

1.)

Find all possible values of c that will make the matrix singluar

(c-1) -2 -3

(c-1) (c+1) -3

0 0 1

i used the formula (a11)(a22)(a33)-(a11)(a32)(a23)-(a12)(a21)(a33)+(a12)(a31)(a23)+(a13)(a21)(a32)-(a13)(a31)(a22)=0

solved it out to get c^2+2c-3=0

thus my roots are 3 and -1(but thats not the correct answer....)

2.)

Let A and B be 3X3 Matrices with det(A)=2 and det(B)=7

i know that for det(AB) you multiply the 2 but i need to find

det(2A)=?

det(3AB)=?

det(AB^-1)=?

3.)

If the determinate of a 4X4 matrix A is det(A)=9, and the matrix D is obtained from A by adding 3 times the third row to the second, determine det(D).

Any help is greatly appreciated

Thank you,

Drew