Question

if x -12y = -210 and x -6y =90, then x=

Answer 1

x - 12y = -210 --------------------------->     x - 12y = -210
x - 6y  = 90 ---->  Multiply by 2 --->  2x - 12y = 180
                           Add together  -->   3x + 0y = -30
                                                           3x = -30
                           Divide by 3 ------> x = -10

Answer 2

(a):  x - 12 y = - 210
(b):  x - 6y   = 90, multiply (2) by - 1 → (c):  -1(x) - (-1)(- 6y) = -1(90)
(c) → -x + 6y = -90

Now add up (a) + (c) ↔ -6y = -300 and y = 50
Plug this value in any of the equation and you'll find  x=390