So you find the moles of the lead nitrate by doing mass/Mr so 25/331.2 which gives you 0.075
Due to stoichiometry in the reaction we see 1:2 ratio so we do 0.075x2 gives 0.15 moles of NaNO3
Then mass: moles x Mr so 0.15 x 85= 12.75g is your theoretical
So % yield is actual/ theoretical x 100
Therefore 6.0g/12.75 g x 100 = 47%
Not sure if it’s correct hope it helps!