x+2y = 8 and 5x+2y = 48

=> \(\left(5x+2y\right)-\left(x+2y\right)=48-8=40\)

=> 4x = 40 => x = 10

=> 10 - 2y = 0 => 2y = 10 => y = 5

So the answer is: \(\dfrac{10+5}{2}=\dfrac{15}{2}\)

As off topic we have :

5x+10y\(-5x-2y=80-48\)

\(\Rightarrow8y=32\)

\(\Rightarrow y=4\)

And x-2y=0

So x = 8

So \(\left\{{}\begin{matrix}x=8\\y=4\end{matrix}\right.\)