Calculate the percentage of the $360 that she spent on presents for her sisters.

Tax amount = $24\%$ of \32,000$Tax amount =$0.24 \times $32,000$Tax amount =$$7,680$The amount she paid in tax in 2018 is$\boxed{$7,680}$.

Increase = $7\%$ of \32,000$Increase =$0.07 \times $32,000$Increase =$$2,240$

Earnings in 2019 = Earnings in 2018 + Increase
Earnings in 2019 = \32,000 + $2,240$Earnings in 2019 =$$34,240$Her earnings in 2019 are$\boxed{$34,240}$.

18. (b) Gretal invests $5 000 at a rate of 2% per year compound interest. Calculate the value of her investment after 3 years.

The formula for compound interest is $A = P(1 + r)^t$, where:
$A$ = final amount
$P$ = principal amount ($5\,000)$r$= annual interest rate (2$t$ = number of years (3)

$A = \$5\,000(1 + 0.02)^3$ $A = \$5\,000(1.02)^3$ $A = \$5\,000 \times 1.061208$ $A = \$5\,306.04$ The value of her investment after 3 years is \boxed{\5,306.04}$.

18. (c) One month, Gretal spent a total of $360 on presents.** **She spent$\frac{1}{5}$of this total on presents for her parents.** **She spent$\frac{2}{3}$of the remaining money on presents for her friends.** **She spent the rest of the money on presents for her sisters.** **Calculate the percentage of the$360 that she spent on presents for her sisters.

Amount for parents = \frac{1}{5} \times \360 = $72$.

Remaining money = \360 - $72 = $288$.

Amount for friends = \frac{2}{3} \times \288 = $192$.

Amount for sisters = Remaining money - Amount for friends
Amount for sisters = \288 - $192 = $96$.

Percentage for sisters = $\frac{\text{Amount for sisters}}{\text{Total spent}} \times 100\%$
Percentage for sisters = \frac{\96}{$360} \times 100%$Percentage for sisters =$0.2666... \times 100%$Percentage for sisters =$26.66...%$

Percentage for sisters $\approx 26.7\%$
The percentage of the $360 that she spent on presents for her sisters is$\boxed{26.7%}$.