"Simplify, then evaluate each expression"

[Sui_Generis]

I'm desperate. I'm not a cheat. But I need someone to do this so that I can see how it's done. I TRIED. I'm totally stuck, and the answer page doesn't show jack. Please, I'm desperate. I asked like 5 people, and everyone tells me, "just substitute the letters for the numbers". Okay, I KNOW but, hello! This is a complex question, and there's like 3 letters beside each other! OMG HELP PLEASE.

This is it: Find the value of 3y(2xz+2) - 6xyz when x = -4, y = -3, and z = 7.

Oh and I KNOW it's done like this,
= 6xyz + 6y - 6xyz
= 6y
= 6 (- 3)
= - 18

But this makes no sense to me. I mean, I stare at it and I stare at it. I went through 3 coffees staring at this question. I can't figure it out. Can someone offer any type of explanation? I'd be so grateful. I'm self-teaching. I'm taking my GED tests. Please, please.

 

[Ishuda]

Every once in a while you get problems like this to try to trip a person up. You would get the same answer if you did
3 * (-3) * (2 * (-4) * 7 + 2) - 6 * (-4) * (-3) * 7
= 3 * (-3) * (-56 + 2) - 6 * 84
= (-9) * (-54) - 504
= 486 - 504 = -18
but it sure takes a longer time. So part of the lesson you should learn from this problem is that you should always take time to really look at the problem before starting on it.

Along this line, I can remember our teacher passing out a test one time with the instructions 'Read the test before you start it'. At the very bottom of a difficult test was the sentence 'Having looked through the test, write your name at the top and turn in the test'. Some students were there a couple of hours trying to answer all the questions.

 

[Steven G]

Every once in a while you get problems like this to try to trip a person up. You would get the same answer if you did
3 * (-3) * (2 * (-4) * 7 + 2) - 6 * (-4) * (-3) * 7
= 3 * (-3) * (-56 + 2) - 6 * 84
= (-9) * (-54) - 504
= 486 - 504 = -18
but it sure takes a longer time. So part of the lesson you should learn from this problem is that you should always take time to really look at the problem before starting on it.

Along this line, I can remember our teacher passing out a test one time with the instructions 'Read the test before you start it'. At the very bottom of a difficult test was the sentence 'Having looked through the test, write your name at the top and turn in the test'. Some students were there a couple of hours trying to answer all the questions.

Ishuda is 100% correct (as always). You should simplify 1st as things may cancel out and you'll have less calculations to do.
Good job!