we have
10x + 8 y = 20 ------> equation A
10 x + 2 y = -10 ------> equation B
Multiply equation A by -1 both sides
so
-10x-8y=-20 -----> new equation A
Adds new equation A and equation B
\
--------------------
-8y+2y=-20-10
-6y=-30
y=5
Find the value of x
substitute the value of y in equation A or equation B or new equation A
10x + 8(5) = 20
10x+40=20
10x=20-40
10x=-20
x=-2
therefore
the solution is the ordered pair (-2,5)