Реши устно и заполни пропуски

1. [ ] \(: 26\) \(\rightarrow\) [ ] \(\cdot\,12\) \(\rightarrow\) [ ] \(+\,50\) \(\rightarrow\) \(98\) .
2. [ ] \(+\,60\) \(\rightarrow\) [ ] \(: 570\) \(\rightarrow\) [ ] \(\cdot\,21\) \(\rightarrow\) \(42\) .
3. [ ] \(\cdot\,35\) \(\rightarrow\) [ ] \(-\,220\) \(\rightarrow\) [ ] \(\cdot\,160\) \(\rightarrow\) \(4000\) .
4. [ ] \(\cdot\,450\) \(\rightarrow\) [ ] \(+\,900\) \(\rightarrow\) [ ] \(: 15\) \(\rightarrow\) \(750\) .