Each week, you drive 150 miles. your car gets 25 miles to the gallon, and gas prices are $3 per gallon. how much gas money will you spend on gas each week?

Here is the equation you will want to use for how many gallons you will need (I will use the variable "g" to represent gallons of gas):
25g=150
The above equation is showing that you will be able to travel 25 miles for every 1 gallon of gas, and so you need to solve for how many gallons of gas you will need to travel 150 miles. So divide both sides by 25 to get:
g=6
Now use that measurement knowing that the amount of gas you need for a week is 6 gallons to find how much you will spend on gas in a week. Here is the equation you will want to use (I will use the variable "g" again to represent the gallons of gas, and the variable "p" to represent the price you will pay every week for gas):
3g=p
So the above equation shows that you will spend $3 for every gallon of gas, and you need to solve for the price you will pay every week for gas. You already know that you will need to use 6 gallons of gas every week, so replace the variable "g" with 6:
3(6)=p
Now go ahead and multiply the 3 and the 6:
18=p
So now you know that the price you will have to pay every week for gas is $18.
I hope this helps! :D