Question

Can someone help me solve 13 please?

Answer 1

Focus on equation 2 for now. Multiply both sides of that equation by 2 to clear out the fraction.

x = (-1/2)y + 6
2*x = 2*[(-1/2)y + 6]
2x = 2*(-1/2)y + 2*6
2x = -y + 12

Now add y to both sides

2x = -y + 12
2x+y = -y + 12+y
2x+y = 12

We end up getting what equation 1 is saying. Equation 1 and equation 2 are identical equations just written in different forms. They produce the same graph. Therefore, you'll have infinitely many solutions. One line is directly on top of the other one. 

Answer 2

take first equation
2x + y =12
2x =12-y
Now for second equation multiply each term with 2 we get
2×x = 2×(-1/2y) +2×6
2x = -y + 12
or 2x + y=12
As we see both the equations match.......hence infinite values if x and y can be obtained.