These are fractions btw
which unit rate is equivalent to 19 miles per gallon?

three gallons over fifty seven miles
fifty seven miles over three gallons
thirty seven miles over four gallons
four gallons over thirty seven miles

I like using ratios, which are basically fractions, for problems like this.
An important thing to remember is order.
The order here is miles:gallons.
Be sure not to mix this up with gallons:miles, as they are different.
Knowing this, we can automatically eliminate A and D, which use gallons:miles.
The unit rate ratio is 19:1, or 19 miles per gallon.
If there are 3 gallons, you are multiplying gallons by 3 so multiply miles by 3.
19 • 3 = 57
This means the ratio when there are 3 gallons is 57:3.
This fits B.
But it's always important to check every answer just in case.
If there are 4 gallons, that's multiplying both sides by 4.
19 • 4 = 76
1 • 4 = 4
76:4 does not match C.

This means the correct answer is B. 57 miles over 3 gallons.