I dont even know how to explain this, but please help

Both Px + Qy = R and Tx + Uy = V have the same solution (2, 9), meaning the point (2, 9) lies on both lines such that x = 2 and y = 9 makes both equations true.

When you add these equations together, you get

(Px + Qy) + (Tx + Uy) = R + V

→   (P + T ) x + (Q + U ) y = R + V

so the first option is equivalent.

When you subtract the first equation from the second, you get

(Tx + Uy) - (Px + Qy) = V - R

→   (T - P) x + (U - Q) y = V - R

so the third option is also equivalent.

-2x + 7 = 7

subtract 7 from both sides.

-2x = 0

divide both sides by -2.

x = 0