I don’t understand this, can somebody help?

[tex]not \: penny \: or \: dime = quarter \: or \: nickle[/tex]
[tex]p(x) = \frac{13 + 18}{86} = \frac{31}{86} = 0.36[/tex]
[tex]gallons \: for \: car \: 1 = \frac{450}{18} = 25 \: gal[/tex]
[tex]gallons \: for \: car \: 2 = \frac{450}{25} = 18 \: gal[/tex]
[tex]we \: need \: 25 + 18 = 43 \: gallons[/tex]
[tex]43 \times 2.49 = 107.07 \: dollars[/tex]