please help me with this science question

Question

Silver bromide can be "dissolved" by the action of aqueous Na₂S₂O₃ (called "hypo") after any silver that has been "activated" by exposure to light is reduced to metallic silver by another reagent. This process is the basis for the development of black-and-white film. Calculate the mass of hypo necessary to dissolve 42.6 g of AgBr. The equation for the dissolving process is given below.

Answer 1

Your reaction is:

AgBr + 2Na₂S₂O₃ → Na₃[Ag(S₂O₃)₂] + NaBr

Correct?

AgBr, molecular weight = Ag + Br = 187.77 g/mol

Na₂S₂O_3, molecular weight = 2Na + 2S + 3O = 158.11 g/mol, but you have two of them, thus

187.77 AgBr goes with 316.22 of hypo

thus 42.6 of AgBr obviously needs 71.7 grams of hypo