First find the total number of baskets sold: $18+24+21+27=90$. Each basket costs \6$,sothetotalmoneyearnedis$90 \times 6 = 540$.Therefore,thetotalamountearnedis$\$540$.

For a proportional relationship, the ratio of total cost to number of notebooks must be constant. Using any row of the table, the unit rate is $\frac{5.50}{2}=2.75$ dollars per notebook. Checking another row gives $\frac{13.75}{5}=2.75$, so the constant of proportionality is 2.75. Therefore, the total cost for $n$ notebooks is given by $c=2.75n$.

From the table, 5 tickets bring in 60 dollars, so the amount collected per ticket is $\frac{60}{5}=12$ dollars. Checking another row confirms this: $\frac{96}{8}=12$ and $\frac{144}{12}=12$. Since each ticket costs 12 dollars, the total money collected for $t$ tickets is $12t$. Therefore, the correct answer is $12t$.

The number of volunteers increases by 3 each hour: $8\to 11\to 14\to 17$. Starting from 17 volunteers at 4 hours, continue the pattern for 2 more hours: at 5 hours, there are $17+3=20$ volunteers, and at 6 hours, there are $20+3=23$ volunteers. Therefore, the correct answer is $23$.

Let $g$ represent the number of granola bars and $f$ represent the number of fruit cups. Since the shop sold 18 items total, the first equation is $g+f=18$. Since each granola bar costs $2andeachfruitcupcosts$3, the total money collected is represented by $2g+3f=45$. Therefore, the correct system is $g+f=18$ and $2g+3f=45$.