Find y

Given:

\[ \begin{bmatrix} x & x – y \\ 2x + y & 7 \end{bmatrix} = \begin{bmatrix} 3 & 1 \\ 8 & 7 \end{bmatrix} \]

Step 1: Compare Elements

\[ x = 3 \]

\[ x – y = 1 \]

Step 2: Substitute x

\[ 3 – y = 1 \]

\[ y = 2 \]

Verification:

\[ 2x + y = 2(3) + 2 = 8 \quad (\text{correct}) \]

Final Answer:

\[ \boxed{y = 2} \]