Answer:
(A). The the time interval between signals according to an observer on A is 1.09 h.
(B). The time interval between signals according to an observer on B is 1.09 h.
(C). The speed is 0.866c.
Explanation:
Given that,
Time interval = 1.00 h
Speed = 0.400 c
(A). We need to calculate the the time interval between signals according to an observer on A
Using formula of time

Put the value into the formula



(B). We need to calculate the time interval between signals according to an observer on B
Using formula of time

Put the value into the formula



(C). Here, time interval of 2.00 h between signals.
We need to calculate the speed
Using formula of speed

Put the value into the formula






Hence, (A). The the time interval between signals according to an observer on A is 1.09 h.
(B). The time interval between signals according to an observer on B is 1.09 h.
(C). The speed is 0.866c.