You can easily solve this with a 3 way rule (regla de 3). $${\frac{{\mathtt{30}}}{{\mathtt{45}}}} = {\frac{{\mathtt{x}}}{{\mathtt{100}}}} \Rightarrow {\mathtt{x}} = {\frac{{\mathtt{200}}}{{\mathtt{3}}}} \Rightarrow {\mathtt{x}} = {\mathtt{66.666\: \!666\: \!666\: \!666\: \!666\: \!7}}$$
