Hbr + khco3 --> h2o + kbr + co2 if i do this reaction with 30 grams of hbr, how many grams of carbon dioxide will be formed?

16 grams.   
 Looking at the reaction equation, it's evident that for each mole of HBr
consumed, 1 mole of CO2 will be produced. So let's calculate the molar mass
of HBr and CO2 first. 
 Atomic weight hydrogen = 1.00794  
 Atomic weight bromine = 79.904  
 Atomic weight carbon = 12.0107  
 Atomic weight oxygen = 15.999   
 Molar mass HBr = 1.00794 + 79.904 = 80.91194 g/mol 
 Molar mass CO2 = 12.0107 + 2*15.999 = 44.0087 g/mol 
 Moles HBr = 30 g / 80.91194 g/mol = 0.370773461 mol 
 Grams CO2 = 0.370773461 mol * 44.0087 g/mol = 16.317258 g   
 Rounding to 2 significant digits gives 16 grams.

1. and 2. question: in which equation? or i don't understand you, 3. a), 4. c), 5. c), 6. b), 7. d), 8. d) if small number is underlined(behind symbol) , b) if big number is underlined(in front of symbol)9. what is underlined there? 10. c)