If $2^{1998}-2^{1997}-2^{1996}+2^{1995} = k \cdot 2^{1995},$ what is the value of $k$?
$\mathrm{(A) \ } 1 \qquad \mathrm{(B) \ } 2 \qquad \mathrm{(C) \ } 3 \qquad \mathrm{(D) \ } 4 \qquad \mathrm{(E) \ } 5$
$2^{1998} - 2^{1997} - 2^{1996} + 2^{1995}$
Factor out $2^{1995}$:
$2^{1995}(2^{3} - 2^{2} - 2^{1} + 1)$
Simplify:
$2^{1995}\cdot (8 - 4 - 2 + 1)$
$2^{1995}\cdot (3)$
By comparing the answer with the original equation, $k=3$, and the answer is $\text{(C)}.$