One quick question. I know that 5,5 is 5.5 in other places. But what does this mean? "1/1,0"? It looks like you are dividing 1 by 1 but why put it as 1/1,0?

Assuming that 1/1,0 = 1, then

Mulitply both sides by 18:

Multiply out the LHS:

This is evidently not the equation you were supposed to derive, but the method to solve it will be the same.

-Dan