Is 3 over 18 equivalent to 6 over 18?

Answer 1

No.

When creating equivalent fractions both the numerator and denominator must be multiplied by the same number.

To get from 3/18 to 6/18 the numerator has multiplied by 2 but the denominator has been multiplied by 1.

Equivalent fractions are equal. As the denominator is the same, a comparison of the numerators tells if they are equal (and thus equivalent) or not: 3 ≠ 6 → 3/18 ≠ 6/18, thus they are not equivalent.