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.

first, you divide the triangle in two, tô form a retangle triangle. after, using pythagoream theorem:

18^2 = 14^2 + (x/2)^2

(x^2/4) + 196 = 324

x^2/4 = 324 - 196

x^2/4 = 128

x^2 = 512

x = √512

x = √2^9

x = 16√2 cm

i hope i you.