Answer:
a + b = 780
Explanation:
If we subtract the two equations we can ”eliminate“ a and b and find the value of z.
a-a = 0
b-b = 0
-10z = -700
z = 70
now we have to subistitute this value in the two equations
a + b -4(70) = 500
a + b + 6(70) = 1200
a+b - 280 = 500
a + b + 420 = 1200
If we simplify we have
a + b = 780
a + b = 780