To balance an equation you want there to be the same number of each element on both sides
b) CO+O2 yields CO2
Count the number you have of each element on each side
There is one C on both sides but there are three O on the left side but only two on the right side
So you would add coefficients to make the O equal
2CO+O2 yields 2CO2
Now it's balanced because you have 2 C on each side and 4 O on each side
If you need help with any others let me know!