Fthe value of x decreases by 6, how does the value of m(x + 9) change?

start with y= m(x+9)

Use the distributive property:

y= mx+9m

Now you want x to decrease by 6:

so y ' = m(x-6) + 9m

Use distributive property again:

y'= mx - 6m + 9m

y' = (mx+9m) - 6m

y' = y - 6m

So the value of y decreases by 6m.