You can use the distributive property to multiply:
( y )( y² - 2y + 4 ) + ( 2 )( y² - 2y + 4) =
y³ - 2y² + 4y + 2y² - 4y + 8 =
y³ + 8
The -2y² and the 2y² cancel each other, and the 4y and -4y cancel each other out!
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