Time it took Hector to complete 18 miles is given by 18 / 12 = 1.5 hours.
Let the time when Wanda will catch up to Hector be t, then, the distance covered by Hector at the time they meet is 18 + 12t and the distance covered by Wanda at the time they meet is 16t.
Then, 18 + 12t = 16t
16t - 12t = 18
4t = 18
t = 18 / 4 = 4.5
Therefore, Wanda will catch up with Hector after 4.5 hours.