Answer
(a) $\$33449.25$
(b) $\$2549.25$
Work Step by Step
(a) For a given principal $P$, rate $r\%$, and a time period $t$, the amount after simple interest is $p(1+r\% \times t)$.
Note that the time in this formula is in years, so 18 months = 1.5 years.
In this case, this evaluates to $30900(1+\frac{5.5}{100} \times 1.5) = \$33449.25$.
(b) The interest is amount - principal = $\$(33449.25-30900) = \$2549.25$
