\(a)y\times3+y\times12,5=825\)
\(\Rightarrow y\times\left(3+12,5\right)=825\)
\(\Rightarrow y\times15,5=825\)
\(\Rightarrow y=825:15,5\)
\(\Rightarrow y=5\frac{10}{31}\)
\(b)y\times3+y:0,5=12,85\)
\(\Rightarrow y\times3+y:\frac{1}{2}=12,85\)
\(\Rightarrow y\times3+y\times2=12,85\)
\(\Rightarrow y\times\left(3+2\right)=12,85\)
\(\Rightarrow y\times5=12,85\)
\(\Rightarrow y=12,85:5\)
\(\Rightarrow y=2,57\)