If the White Rock Fire Department invests now in new ladder systems for several of its trucks, the department would save $3500 every 6 months in repair costs. What single cash investment made now is equivalent to the repair payments if interest is 8% compounded quarterly and the payments made

a) at the end of every 6 months for 15 years?

b) at the beginning of every 6 months for 10 years?

c) at the end of every 6 months for 8 years but defered for four years?

d) at the beginning of every 6 months for 9 years but defered for 3 years?

e) at the end of every 6 months in perpetuity?

f) at the beginning of every 6 months in perpetuity?