# Linear equation?

#### Jenne3215

##### New member
Is this a linear equation?
I have no idea what my teacher is talking about or asking for can anyone help thanks!

f(x) =-0.12x - 1.4 ?

AND

this word problem is driving me insane!

When going more than 38 mph the gas mileage of a certain car fits the model y=43.81 - .395x where x is the speed of the car in mph and y is the miles per gallon. based on this model at what speed will the car average 15 miles per gallon round to the nearest whole #

#### tkhunny

##### Moderator
Staff member
Jenne3215 said:
Is this a linear equation?

f(x) =-0.12x - 1.4 ?
Yes, it is linear. Look at the exponents on the variables. All one (1)? Linear

When going more than 38 mph the gas mileage of a certain car fits the model y=43.81 - .395x where x is the speed of the car in mph and y is the miles per gallon. based on this model at what speed will the car average 15 miles per gallon round to the nearest whole #
Look at the definitions.

"y is the miles per gallon"

Look at the question.

"average 15 miles per gallon"

Translate in your mind -- That means y = 15

Your task is to solve for x, 15 = 43.81 - 0.395*x