Ratio and Proportion: 15: 1000:: X: 100

First step is to find the least common divisor of the denominators 19, 25, 5 and 15, which is 1425

Next, multiply each fraction with 1425 as follows

\(\frac{4}{19}\)* 1425=300

\(\frac{4}{25}\)* 1425=228

\(\frac{3}{5}\)* 1425=855

\(\frac{3}{15}\)* 1425=285

From the calculations above, 855 is the largest number among the four computed numbers. Then, it follows that\(\frac{3}{5}\) is the largest number.

\(\frac{x}{4}=\frac{9}{x}\)

Cross-multiply the above proportion equation

\(x^2=9\ast4\)

\(x^2=36\)

Take square root on both sides

\(\sqrt{x^2}=\sqrt{36}\)

\(x=\pm6 \ (6\ or\ -6)\)

Taking the positive square root, x=6

Convert the mixed fractions into improper fractions as:

\(7 7/10=\frac{\left(10\ast7\right)+7}{10}=\frac{70+7}{10}=\frac{77}{10}\)

\(3 4/5=\frac{\left(5\ast3\right)+4}{5}=\frac{15+4}{5}=\frac{19}{5}\)

Now, subtract the improper fractions as:

\(\frac{77}{10}-\frac{19}{5}=\frac{77-19\left(2\right)}{10}=\frac{77-38}{10}=\frac{39}{10}\)

As a mixed fraction\(\frac {39}{10}\) becomes\(3 \frac {9}{10}\)

Use the relation 1 gallon= 128 fluid ounces to convert between gallons and ounces. Then,

\(576\ fluid\ ounces\ast\frac{1 gallon}{128 fluid ounces}=4.5 gallons\)