First one subtract 4/5 and 3 3/4 then divide both sides by the number you get from subtracting.
Answer:
The fossil is 1860 years old.
Step-by-step explanation:
The equation for the amount of fossil has the following format:

In which Q(t) is the amount after t years, Q(0) is the initial amount and r is the rate of change.
Half-life of c-14 is 5730 years.
This means that 
So







So

How old is the fossil?
This is t for which

So







The fossil is 1860 years old.
87,240. I added them both together.
Sum= addition