The diagram shows the miles traveled by bikers Alberto and Bjorn. After four hours, about how many more miles has Alberto biked than Bjorn?

$\text{(A)}\ 15 \qquad \text{(B)}\ 20 \qquad \text{(C)}\ 25 \qquad \text{(D)}\ 30 \qquad \text{(E)}\ 35$
After 4 hours, we see that Bjorn biked 45 miles, and Alberto biked 60.  Thus the answer is $60-45=15$ $\boxed{\text{(A)}}$.