An observer moves at 0.60 c relative to a frame in which clock C is at rest. After accounting for the time that light signals take to travel from clock C, the observer deduces that clock C advances 4.0 s in a certain interval. What is the time measured by a clock at rest in the observer's frame?

A) 2.4 s
B) 3.2 s
C) 5.0 s
D) 6.4 s