Start by multiplying 38 times 4 (38 gallons of gas times four days)
38 x 4 = 152
He used 152 gallons of gas over 4 days.
Now, multiply 152 by 2.17 to find out how much it cost.
152 x 2.17 = 329.84
This man used $329.84 of gas in four days.
Best of luck.