Answer: 390
Step-by-step explanation: Well if its 30 miles per gallon and you have 13 gallons do 30*13 which is 390

so
(this is wrong because
)
you didn't tell wich program to use and did not include any pictures.
anyways, I graphed the function with desmos (free to use as app and on website)
so that u can see what the graph should look like.
variance based on the zoom is okay of course.
You divide 3 by 8 to get an answer of 0.375, next you want to multiply 0.375 x 100 to get an answer of 37.5... that number is your percentage 3/8 is a 37.5%