Answer:
5.74 g
Step-by-step explanation:
Using conservation of mass:
mass of the reactant = mass of the product if the system is closed
 but in this case the bubbles must have been allow to leave the solution and the resulting mass after the reaction equals 64.96 g 
to find the mass of Co2 released 
we subtract mass of the remaining product from the mass of the reactant 
mass of reactant =14 g + 56.70 = 70.7 g
mass of carbon dioxide = 70.7 - 64.96 ( mass of the remaining product after the bubble) = 5.74 g