Lena drove 355 miles using 17 gallons of gas. At this rate, how many gallons of gas would she need to drive 284 miles.

13.6 gallons

Step-by-step explanation:

Miles Driven = Gallons Burnt * Miles Per Gallon

So if yo drive 20.88 miles on one gallon how many gallons does it take to drive 284 miles.  This is 284/20.88 = 13.6 gallons

Whilst the numerical answer is correct the previous answer, it does not maintain the validity of the units - in which things are measured.  You will see this is very important in science

What can we learn from this.  As an intermediate step we have learnt that the car does 20.88 mpg, lets call it 21.  So a car that has a sticker at the show room with an MPG of more than 21 will consume less gas and one that has a smaller mpg will consume more.