Answer:

Explanation:
Let's use the decay equation.

Where:
- A is the activity at t time
- A₀ is the initial activity
- λ is the decay constant
We know that 
So we have:




Therefore, the half-life of the source is 6 hours.
I hope it helps you!
I assume these are scientific notation thus 10^x not 10x
first multiply all numbers together
so 2.5*10^4*3*10^2
or 25000*300
so you get 7500000.0
move the decimal to 7.5
which is 6 places
the answer is c 7.5*10^6
Answer:
non of the above
Explanation:
Quantity of heat = mass× specific heat× change in temperature
m= 7kg c= 4.18 temp= 46-25=21°
.......H= 7×4.18×21= 614.46kJ