a$.15\%$ nominal rate, semiannual compounding, discounted back $6$ years. Do not round intermediate calculations. Round your answer t

nearest cent.

$

b$.15\%$ nominal rate, quarterly compounding, discounted back $6$ years. Do not round intermediate calculations. Round your answer to $t$

cent.

$

c$.15\%$ nominal rate, monthly compounding, discounted back $1$ year. Do not round intermediate calculations. Round your answer to the

cent.

$

d$.$ Why do the differences in the PVs occur?