Hey there Jovenah :)
So to solve this problem, you would need to find how much 14 gallons of gasoline would cost and how much 3 gallons of oil would cost. To do this, you can make two equations for the gasoline and the oil.
You are already given the amount of money it would cost for one gallon of gasoline and for one gallon of oil, so all you need to do is multiply the number of gallons that Mary is going to buy by the price for each gallon of gasoline or oil.
Number of gallons Mary is going to buy:
You are given that Mary will buy 14 gallons of gasoline and 3 gallons of oil. You are also given that each gallon of gasoline is sold at $1.19 per gallon and each gallon of oil is sold at $2.25 per gallon. Now you can create two equations with this given information.
Your two equations should look like:
14g and 3o, where g is gallons of gasoline and o is gallons of oil. Knowing the price per gallon of gasoline and oil, you can plug them in for g and o.
You can plug $1.19 for g (price per gallon of gasoline) and $2.25 for o (price per gallon of oil). Now your equations should look like:
14($1.19) and 3($2.25); now you can multiply the numbers and find out how much Mary spent for the gallons of gasoline and the oil.
14 × $1.19 = $16.66
3 × $2.25 = $6.75
After solving the two equations, you can now see that Mary spent $16.66 on 14 gallons of gasoline and $6.75 on 3 gallons of oil. To find out the total amount of how much Mary spent, add the amounts that she spent for the gasoline and oil.
$16.66 + $6.75 = $23.41
You can now see that Mary spent a total of $23.41 on 14 gallons of gasoline and 3 gallons of oil. Your answer to this problem is $23.41.
Hope this helped you! :)