so when you have ratios, some are unknowns you have to create complex fractions from them. Bring to the same donominator, and solve for x.
Ex: we have this portion:
2 -x
5-45
and we change it into fractions
2/5 =x/25
2x9/5x9 = x/45
answer would be 18=x
in case of more complex fractions it may become in handy.
Your welcome!!