Answer: C
Step-by-step explanation:
To multiply a number (outside of a matrix), simply distribute that number to EVERY value of the matrix.
[tex]X\left[\begin{array}{cc}a&b\\c&d\end{array}\right] \quad = \quad \left[\begin{array}{ccc}a(X)&b(X)\\c(X)&d(X)\end{array}\right] \\\\\\3\left[\begin{array}{cc}-2&0\\4&-7\end{array}\right] \quad =\quad \left[\begin{array}{cc}-2(3)&0(3)\\4(3)&-7(3)\end{array}\right]\quad = \quad \large\left[\begin{array}{cc}-6&0\\12&-21\end{array}\right][/tex]
