Answer:
20 weeks is your answer because you decide by time I think
For this case we have the following expression:

To verify the answer we have:
Multiplying both sides of the equation by -14:

Thus, the answer can be verified with:

Answer:

A=x(1+r/n)^nt
21150=x(1+0.032/12)^84
21150=x(1+0.0026666)^84
21150=x(1.002666666)^84
21150=x(1.25069809)
21150/1.25069809=x
16910.56=x
Hope this helps!
Here you go this took me time