Answer:
FeS + 2HBr ---> FeBr2 + H2S
Step-by-step explanation:
Judging from the subscripts on the right hand side of the given forward reaction Br has 2 molecules and Hydrogen also has 2 molecules.
next we rewrite the equation in a "balanced" manner to equate both the left and right hand side with each other.
tip: be careful of multiplications of subscripts with the coefficient of the given compound to avoid balancing errors.