The answer is -54
When you look at the first equation and the second one you can see that the variables arent in the same order. So you first have to change that.
-48a-42b-6c is now written the same way
Now you aha e to look for the rate of change
-48/8 =-6
-47/7=-6
-6/1=-6
All of them show that the rate of change was -6 so you just have to multiply the 9 by -6 to get your answer which is -54
