Answer:
The cost of 15 liters is $31.50
Step-by-step explanation:
1. Find the price for 1 liter of petrol.
Divide the cost by the number of liters:
$14.70 / 7 = $2.10 per liter.
2. Multiply the price for 1 liter by the new number of liters, 15.
$2.10 per liter x 15 liters = $31.50
First you must acknowledge that you are dealing with a line therefore you must write linear equation or linear function in this case.
Linear function has a form of,

Then calculate the slope <em>m</em> using the coordinates of two points. Let say <em>A(x1, y1)</em> and <em>B(x2, y2)</em>,

Now pick a point either <em>A</em> or <em>B</em> and insert coordinates of either one of them in the linear equation also insert the slope you just calculated, I will pick point <em>A</em>.

From here you solve the equation for n,

So you have slope <em>m</em> and variable <em>n</em> therefore you can write down the equation of the line,

Hope this helps.
r3t40
Ok so basically you have to anahajahabdbnxnxkskalakand
The y-value must be the numerator.
The correct way of solving this would be (7-10)/(3-5)=3/2