10x-12 is the answer I believe
The distance is 6 I think
if its diameter is 8 cm, then its radius is half that, or 4 cm.

We need to write a proportion to solve this
7/3=35/x
105=7x
divide each side by 7
15=x so, there were 15 burgers without cheese.
We could add the cheese burgers 35 to burgers without cheese 15
35+15=50 burgers were sold.