Adeline, Bonnie, and Cathy are walking along a long flat path, with their initial distances shown below.
[asy]
size(10cm);
draw((0,0)--(12,0)--(28,0));
label("Adeline",(0,1));
label("Bonnie",(12,1));
label("Cathy",(28,1));
label("12 miles",(6,-1));
label("16 miles",(20,-1));
dot((0,0));
dot((12,0));
dot((28,0));
[/asy]
Adeline and Bonnie walk towards each other at constant speeds of 1 and 2 miles per hour, respectively. Cathy walks in the same direction as Bonnie. If all three girls meet each other at the same time, what is Cathy's walking speed, in miles per hour?<spanclass=′latex−bold′>(A)</span>4mph<spanclass=′latex−bold′>(B)</span>4.5mph<spanclass=′latex−bold′>(C)</span>5mph<spanclass=′latex−bold′>(D)</span>5.5mph<spanclass=′latex−bold′>(E)</span>6mph