What is the present value of the$$ following?

a$.$ What is the present value of a $$550$ perpetuity discounted back to the present at $6$ percent?

b$.$ A $$$$6000$ perpetuity discounted back to the present at $10$ percent?

c$.$ A $$$$240$ perpetuity discounted back to the present at $7$ percent?

d$.$ A $$$$75$ perpetuity discounted back to the present at $3$ percent?