$($Compound annuity$)$ What is the accumulated sum of each of the following streams of payments?

a$.$ $$500$ a year for $8$ years compounded annually at $10$ percent.

b$.$ $$104$ a year for $7$ years compounded annually at $9$ percent.

c$.$ $$32$ a year for $12$ years compounded annually at $11$ percent.

d$.$ $$21$ a year for $6$ years compounded annually at $6$ percent.