Look, this shouldn't be that hard. As long as you know the symbol for each element, you just put a subscript to indicate how many there are in each compound.
For the second row, there is one C and 4 H's. That's [tex]CH_4[/tex], or methane.
For the third row, there is one Si and 2 O's. That's [tex]SiO_2[/tex], or common glass/quartz.
