Answer:
This is a typical radioactive decay problem which uses the general form:
A = A0e^(-kt)
So, in the given equation, A0 = 192 and k = 0.015. We are to find the amount of substance left after t = 55 years. That would be represented by A. The solution is as follows:
A = 192e^(-0.015*55)
A = 84 mg
Amount of clay used = volume of the sphere
It is given that the radius of the sphere is 2 inches.
Volume of the sphere = 



Hence, the amount of modeling clay Terrence used
cubic inches.
9.9^2X1.79
9.9^2=98.01
98.01X1.79=175.4379
N=2p
(n+7) + (p+7) = 68
2p + 7 + p + 7 = 68
3p + 14 = 68
3p = 68 - 14 = 54
p=54/3=18
n=2p=36
Check: (18+7)+(36+7)=25+43=68 good