Answer: she made a mistake between 1 and 2
Answer:
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Answer : The substances half life in days is, 5.6 days.
Step-by-step explanation :
Half life : It is defined as the amount of time taken by a radioactive material to decay to half of its original value.
All radioactive decays follow first order kinetics.
The relation between the half-life and rate constant is:

where,
k = rate constant = 0.1235 per days
= half-life
Now put all the given values in the above formula, we get:


Thus, the substances half life in days is, 5.6 days.
Just do 7/4 and cross multiply with 1/2