During which phase of the cell cycle are chromo-
somes copied?

S phase

Explanation:

S phase is the second phase of interphase (longest phase where cell grows and replicates it's DNA and does it function. It is broken up into smaller sub phases). S phase is the synthesis phase. During this phase chromosomes are replicated ( The DNA is copied).

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

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