i was practicing some advanced level questions and i came across this one

On heating with soda lime, sodium ethanoate decomposes in accordance with the following eqn

CH3COONa + NaOH ----> CH4 + Na2CO3

iF 8.2g of sodium ethanoate produced 560 cm^3 of methane (at stp (standard temp. and pressure) what is the percentage yield?

they have the answer as

25.0