Answer:
approximately 27 grams
Work Shown:
Half life formula
y = A*(0.5)^(x/H)
where,
A = starting amount = 30 grams
H = half life period = 90 years
x = number of years that pass by = 12
y = amount left over after x years
Let's plug the values for x, A and H into the formula to find y
y = A*(0.5)^(x/H)
y = 30*(0.5)^(12/90)
y = 27.3516746567466
y = 27 .... rounding to the nearest whole number
The two in the hundredths place is ten times less than the two in the tenths place.
X = number of servers
y = number of guests

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There must be at least 1 server for every 12 tables:
<h3>
Answer: 168 square cm</h3>
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Work Shown:
- L = 2 = length
- W = 6 = width
- H = 9 = height
The order of length, width and height doesn't matter
SA = surface area of rectangular prism
SA = 2*(LW + LH + WH)
SA = 2*(2*6 + 2*9 + 6*9)
SA = 2*(12 + 18 + 54)
SA = 2*(30+54)
SA = 2*(84)
SA = 168 square cm