I believe you meant to ask how much gas does he use in 4.2 hours
we first need to calculate how much he uses in 1 minute.
60 min = 0.4 gallons
1 min = x
where x is the amount of gallons used per minute.
we cross multiply this equation:
60 x = 0.4
x = 0.4/60
we leave it is for now.
How many minutes are in 4.2 hours?
4 (60) + 0.2 (60) = y
where y is the number of minutes found in 4.2 hours. So after expanding the equation we have:
240 + 12 = y
252 = y
Now we multiply this number of minutes by the amount of gallons used for each minutes to get the total amount of fuel used.
252 * 0.4/60 = ?
100.8/60 = ?
100.8 divided by 60 = 1.68
Therefore in 4.2 hours, he uses 1.68 gallons of gasoline.