AHSME 1996 Problem 8

If $3 = k\cdot 2^r$ and $15 = k\cdot 4^r$, then $r =$ $\text{(A)}\ -\log_{2}5 \text{(B)}\ \log_{5}2 \text{(C)}\ \log_{10}5 \text{(D)}\ \log_{2}5 \text{(E)}\ \frac{5}{2}$