im using

Fv=pv x ($1+r/c)^n-1/(r/c)

pv=fv x 1/($1+r/c)^n-1/(r/c)

fv=Ann x ($1+r/c)^n

pv=ann x ($1-$1/($1+r/c)^n/(r/c)

i dont know which one to use

2. How much must you invest today to receive $3,000 per month for twenty months (starting one month from today) if you can earn 6% annual interest