Answer
(a) It took 567 seconds for a one-way transmission from Spirit.
(b) It took 662 seconds for scientists to communicate with Opportunity.
Work Step by Step
(a) The rovers communicate with scientists on Earth by sending radio waves.
We can find the time of a one-way transmission from Spirit:
$t = \frac{d}{c}$
$t = \frac{170.2\times 10^{9}~m}{3.0\times 10^8~m/s}$
$t = 567~s$
It took 567 seconds for a one-way transmission from Spirit.
(b) We can find the time required for scientists to communicate with Opportunity:
$t = \frac{d}{c}$
$t = \frac{198.7\times 10^{9}~m}{3.0\times 10^8~m/s}$
$t = 662~s$
It took 662 seconds for scientists to communicate with Opportunity.
