Gas costs $3.89 for unleaded and $4.09 for premium. if i buy 37 gallons of gas for $148.93, how much of each type of gas do i buy?

Let the number of gallons of the unleaded is x and for the premium is y
x + y = 37 > x = 37 - y

3.89x + 4.09y = 148.93
3.89(37-y) + 4.09y = 148.93 
143.93 - 3.89y + 4.09y = 148.93
1/5 y = 5

y = 25 gal , x = 12 gal

31 is prime. and it’s prime factorization is just 31.