Question 896560
270/6=45 mpg
675/45=15 gallons  at 45 mpg 
or 

270/6=675/x
Don't cross multiply yet. Divide by 45
270/45=6
675/45=15
6/6=15/x
x=15
or 
270/6=45
45=675/x
45x=675
x=15