Hi I am working out of the Prealgebra 7th Edtion iSBN 032199

Hi I am working out of the Prealgebra 7th Edtion iSBN: 0-321-99715-8
I am on chapter 2.7 and problem 32.

This is the problem as I have it worked out on my paper:
3x⁴-2y⁴+8x⁴y⁴-7x⁴+y⁴ = (3x⁴-7x⁴)+(-2y⁴+y⁴)+8x⁴y4
= -4x⁴+y⁴+8x⁴y⁴

Now that is the answer that I get, but when I look at the guided solutions page, it tells me the answer is -4a⁶-3b⁴+2a⁶b⁴  ...... where did the a⁶ or the b⁴ or the a⁶b⁴ part come from?? And how is -2y⁴ + y⁴ equal 3?? -2 + 1 is -1 ?? Please show me step by step and explain everything because I am so super confused.

Thanks

Solution

You have done it right just put - sign in front of y4. But be answer is wrong or you have skipped some information given in question.