(a) John is at $B$, on a straight beach, 10 miles from $A$. Mary is in a boat in the sea at $C, 4$ miles from the beach (see Figure 12 ). Assuming Mary can row at 3 miles per hour and jog at 5 miles per hour, where along the beach should she land so that she may get to John in the least amount of time? Solve the problem if John is (b) 100 miles; (c) 1 mile from $A$.