5a) \[ \begin{array}{l} x+y=3 \\ x-y=7 \end{array} \]

Step 1 ：\(\begin{array}{l} x+y=3 \\ x-y=7 \end{array}\)

Step 2 ：Add the two equations to eliminate one of the variables:

Step 3 ：\(x+y+(x-y)=3+7\)

Step 4 ：\(2x=10\)

Step 5 ：Solve for x:

Step 6 ：\(x=\frac{10}{2}\)

Step 7 ：\(\boxed{x=5}\)

Step 8 ：Substitute the value of x into one of the original equations:

Step 9 ：\(5+y=3\)

Step 10 ：Solve for y:

Step 11 ：\(y=3-5\)

Step 12 ：\(\boxed{y=-2}\)

Step 13 ：Final Answer: \(\boxed{x=5, y=-2}\)