Answer:
length = 60m
Step-by-step explanation:
let '3x' = length
let '2x' = width
3x + 3x + 2x + 2x = 200
10x = 200
x = 20
length = 3x = 3(20) = 60
So what do you need us to do for you?
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:
