Trend lines can be used to make
predictions in real-world situations.
Three methods for making trend lines
are:
method (by hand)
• divide-center method (by hand)
regression (with
technology)

a + b = 780

Step-by-step 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