Answer:
1770
Explanation:
No calculator is needed.
When you fill in the numbers, you get ...
1 = (x/1770)^(-0.8)
The only way the value will be 1 is if the fraction is 1:
x/1770 = 1
The only way the fraction will be 1 is x = 1770.
1770 mg Zn ions per liter will be lethal in 1 minute.
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Check
You know the answer will be slightly more than 1743 from your answer to the second part of the first question.