You can
put this solution on YOUR website!lets call the number of liters sold of 61.9c and 54.9c gas, s and f respectively
:
s+f=50000...........eq 1
.619s+.549f=29000...eq 2
:
lets rewrite eq 1 to s=50000-f and plug that value into eq 2
:
.619(50000-f)+.549f=29000
:
30950-.619f+.549f=29000
:
-.07f=-1950
:

liters of 54.9 c gas
:

liters of 61.9 c gas