First find the price per ounce of the 12-ounce bottle: $\frac{2.40}{12}=0.20$ dollars per ounce. Then multiply by 20 ounces: $0.20\times 20=4.00$. So the larger bottle should cost $4.00$.

Since the solution is $15\%$ salt, the amount of salt in $x$ milliliters is $15\%$ of $x$, or $0.15x$. The mixture contains $24$ milliliters of salt, so set the salt amount equal to $24$: $0.15x=24$. Therefore, the correct equation is $0.15x=24$.

Since $1$ liter equals $1,000$ milliliters, multiply $0.75$ by $1,000$:

So $0.75$ liter is equivalent to $750$ milliliters.

From the graph, the cyclist travels 12 miles in 3 hours, so the unit rate is $\frac{12}{3}=4$ miles per hour. Since 1 mile is 100% of a mile, 4 miles is $4\times 100\%=400\%$ of a mile. Therefore, the correct answer is $400\%$.

If orange juice was $40\%$ of the total, then apple juice was the remaining $60\%$. The problem says that this $60\%$ equals $18$ liters. Let $t$ be the total number of liters ordered. Then $0.60t=18$. Solving gives $t=\frac{18}{0.60}=30$. So the school ordered $30$ liters in all.