It is given in the question that
The gas tank of Tyrell's truck holds 19.8 gallons. when the tank empty, Tyrrell fills it with gas that costs $3.65 per gallon.
It means cost of one gallon of gas is $3.65 .
And the tank hold 19.8 gallon . So cost of 19.8 gallon is
Therefore about $72.27 it will cost to fill the tank .