HELP I"M BEING TIMED! (also giving brainiest to the correct one and don't answer just for points.)

Katya and Alec completed these steps to find the sum of Three and five-sixths and .

Katya's work. 3 and 5-sixths plus 1-fourth. 3 StartFraction 5 times 2 over 12 EndFraction plus StartFraction 1 times 3 over 12 EndFraction. 3 and 10-twelfths plus 3-twelfths. 3 and 13-twelfths. 4 and 1-half. Alec's work. 3 and 5-sixths plus 1-fourth. 3 StartFraction 5 plus 4 over 10 EndFraction plus StartFraction 1 plus 6 over 10 EndFraction. 3 and 9-tenths plus 7-tenths. 3 and 16-tenths. 4 and 6-tenths.

Which best describes the correct sum?

Katya is correct because 12 is the only common denominator that can be used to find this sum.
Katya is correct because Ten-twelfths is equivalent to Five-sixths and Three-twelfths is equivalent to One-fourth.
Alec is correct because the common denominator is the sum of 6 and 4.
Alec is correct because Nine-tenths is equivalent to and is equivalent to Seven-tenths.