As measured by observers on Earth, two stars, A and B, undergo supernovae. First, star A explodes, and 2.0 years later, a second explosion is detected from star B. A distance of 5.0 ly separates the two stars. Assume the explosion of A occurs at X_A=0 and t_A=0. Two scientific spacecraft (SC1 and SC2) are traveling from A to B at a constant velocity of 0.25c and 0.40c. When star A explodes, SC1 and SC2, positioned at the origin of their respective reference frames, coincidentally pass by A. Determine the time difference between the two explosions detected by the SC1 and SC2 crews.