This is a simple interest problem, the formula is 

A = P(1 + rt) P = principal, r = rate, t = time

1.) $200 at 4.5% for 8 years

A = 200(1 + (.045 * 8))
= 200(1.36)
= $272

2.)$450 at 4% for 1/2 year (.5 year)

A = 450(1 + (.04 * .5))
= 450(1.02)
= $459

3.) $20,000 at 9.6% for 8 months (.67 years)

A = 20,000(1 + (.096 * .67))
= 20,000(1.06432)
= $21,286.40

4.) $400 at 3% for 1 month (.08 years)

A = 400(1 + (.03 * .08))
= 400(1.0024)
= $400.96