4. When Cheney was a child, he could walk 15 miles in 3 hours and 30 minutes. Now that he is an old man, he can walk 10 miles in 4 hours. Compared to when he was a child, he now takes ( ) more minutes to walk 1 mile.
(A) 6
(B) 10
(C) 15
(D) 18
(E) 30
4. B.
$$
\frac{4 \times 60}{10}-\frac{3 \times 60+30}{15}=10 \text{.}
$$