The largest number is 952. I'll tell you why...
7*8=56
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56*18=7*8*18=7*8*3*6=1008 (4 digits)
56*17=7*8*17=952 (3 digits)
B -222
Because he fell/descended 222 meters. And falling or going down produces a negative integer. Also, if you were actually doing the math to try to find where Oliver is currently located, you wouldn't add 222, or 0, or subtract -444. You would subtract 222.
In addition, be aware that the question is asking you an integer to represent a situation, not the answer of where Oliver is.
Given:
Initial mass, m₀ = 23 g
Decay constant, k = 0.13
Exponential decay obeys the equation

where t = time, days
For half life, the mass is m = m₀/2.
Therefore

Answer: The half life is 5.33 days
You can first take out an x^2 from each number , 3x^6 - 39x^4 + 108x^2 = x^2 ( 3x^4 - 39x^2 + 108) Then just factor and solve for the zero's of the equation