The ratio of blue paint to white paint is constant for the same shade. From the table, $\frac{3}{5}=\frac{6}{10}=\frac{9}{15}$, so the ratio is $\frac{3}{5}$. For a batch with 24 cups of white paint, let $b$ be the number of cups of blue paint. Then

Multiply both sides by 24:

So 14.4 cups of blue paint are needed.

The original ratio of flour to sugar is $3:2$. To keep the same ratio when using 15 cups of flour, multiply both parts of the ratio by 5, since $3\times 5=15$. That gives $2\times 5=10$ cups of sugar. But the baker uses 12 cups of sugar, which is 2 cups more than needed to keep the ratio the same. Therefore, the mixture has a greater proportion of sugar than the original recipe, so it must be too sweet compared with the original. Choice A is correct.

Because the tank is cylindrical and has the same diameter throughout, the volume of water is directly proportional to the water depth. So the ratio of gallons to inches stays constant. At 18 inches, the tank contains 54 gallons, so there are $\frac{54}{18}=3$ gallons per inch of depth. At 30 inches, the amount of water is $30\cdot 3=90$ gallons. Therefore, the correct answer is $90$.

From the table, 3 cups of pretzels make 8 cups of total mix, so the recipe uses a constant ratio. That means the total mix is $\frac{8}{3}$ times the amount of pretzels. For 15 cups of pretzels, the total mix will be $15\cdot \frac{8}{3}=40$ cups. The peanuts are the part of the mix that is not pretzels, so cups of peanuts $=40-15=25$. Therefore, the correct answer is 25.

The final flour-to-sugar ratio must be $5:3$. Since there are 18 cups of sugar, the amount of flour in the final mixture must satisfy

Solving gives

So after the extra 7 cups are added, there are 30 cups of flour. Therefore, before those 7 cups were added, there were

cups of flour. So the correct answer is $23$.