Answer is 7, can someone explain me how they got 7.

68) Project Test Bank is composed of activities we will refer to as A, B, C, and D for convenience (and lack of creativity). Durations and precedence requirements are shown in the table. Each of these activities can be conveniently laddered into two sub-activities of equal duration, so activity C in the original project becomes two activities, C1 and C2, each of which lasts 7 days. The first half of each activity serves as the predecessor to its second half and the first half of the original following activity. What is the difference in the late start time for activity C in the original project and activity C1 in the laddered project? Activit edecessor en 10 18 14 20