Answer:
The substance half-life is of 4.98 days.
Step-by-step explanation:
Equation for an amount of a decaying substance:
The equation for the amount of a substance that decay exponentially has the following format:
In which k is the decay rate, as a decimal.
k-value of 0.1392.
This means that:
Find the substance's half life, in days.
This is t for which 
. So
The substance half-life is of 4.98 days.
I think it’s the last one
Explanation: If a pyramid and a prism have the same base and height, their volumes are always in the ratio of 1:3 . As volume of prism is 108 cubic meters, volume of pyramid is 13×108=36 cubic meters.
Answer: 6 hours
Step-by-step explanation: If you write an equation for this scenario it would be y = 12+3x. 12 is the starting value and x represents how many hours the bike is rented, therefore 3 dollars would be added to the initial 12 each hour. So if Lucy spent $30 then it would change to 30= 12+3x. Now you essentially just need to work backwards. Rearrange the equation and move 12 to the left of the equal sign to make 30-12=3x. Combine vairable to make 18=3x. Divide 3x by 3 to isolate x and divide 18 by 3 as well to make it even. This looks like 18/3=3x/3. Meaning it would end up as 6=x.
