[3375:(507-6x)+91]*7-2*309=41*2
[3375:(507-6x)+91]*7-618=82
[3375:(507-6x)+91]*7=618+82
[3375:(507-6x)+91]*7=700
3375:(507-6x)+91=700:7
3375:(507-6x)+91=100
507-6x+91=3375*100
507-6x+91=337500
507-6x=337500-91
507-6x=337409
6x=337409-507
6x=336902
x=336902/6
x=5615