$($Present value$)$ What is the present value of the following future amounts?

a$.$What is the present value of $$$$600$ to be received $9$ years from now discounted back to the present at $10$percent$?$

b$.$ $$400$ to be received $8$ years from now discounted back to the present at $7$ percent?

c$.$ $$1,000$ to be received $12$ years from now discounted back to the present at $5$ percent?

d$.$ $$1,100$ to be received $6$ years from now discounted back to the present at $20$ percent?