Final answer:
The inequality to describe how much battery life Larissa's watch has left after being on for 12 hours is t + 12 ≤ 20, where t is the number of hours the watch can continue to run. The watch can run for at most 8 more hours before the battery is depleted.
Step-by-step explanation:
When Larissa's watch is fully charged, it can last for up to 20 hours before running out of battery. Since it has been 12 hours since the watch was fully charged, we want to describe how much battery life could be left. We can write an inequality to represent the situation as follows:
t + 12 ≤ 20
where t represents the number of hours the watch can continue to run. This inequality shows us that the remaining battery life, plus the 12 hours already passed, should be less than or equal to the total battery capacity of 20 hours. To complete the sentence we could say: "The watch can run for at most 8 more hours before the battery runs out."