125 MPH = 125/60 MP(Minute) because 1 Hour = 60 Minutes
= 2.0833...Miles per minute
Answer:
a)
, b)
, c)
, d) 
Step-by-step explanation:
a) Let assume an initial mass m decaying at a constant rate k throughout time, the differential equation is:

b) The general solution is found after separating variables and integrating each sides:

Where
is the time constant and 
c) The time constant is:


The particular solution of the differential equation is:

d) The amount of radium after 300 years is:

Do you mean 3 to the third power or three times three? Three to the third power would be three times three times three which is 27. But just three times three is 9