All you have to do is look at the graph.
5 gallons of gas is $8.80, let’s figure out how much one gallon is. 8.80/5=$1.76.
1.76•6=10.56 check
1.76•7=12.32 check
Now let’s figure out how much 10 gallons of gas cost.
1.76•10=17.6
10 gallons of gas costs $17.60