Answer:
The age of the spear head is of 1938 yers.
Explanation:
The amount of carbon 14 after years is given by the following equation:

In which Q(0) is the initial amount and r is the decay rate.
The half life of carbon 14 is 5700 years.
This means that

So








So

We have to find:
t for which Q(t) = 0.79Q(0). So








Rounding to the nearest year.
The age of the spear head is of 1938 yers.