To find the remaining amount of gasoline, we start with the amount of gasoline Frank bought and subtract the amount he used.
- Frank bought 3 gallons of gasoline.
- He used \( \frac{3}{4} \) of a gallon.
To find the remaining amount, we can perform the following calculation:
\[ 3 - \frac{3}{4} \]
We can convert 3 to a fraction with a denominator of 4:
\[ 3 = \frac{12}{4} \]
Now we can subtract:
\[ \frac{12}{4} - \frac{3}{4} = \frac{12 - 3}{4} = \frac{9}{4} \]
So the remaining amount of gasoline is \( \frac{9}{4} \) gallons.
The answer is \( \frac{9}{4} \).