1. The same three letters, in the same order, will change each of the words below into new ones:

HER
ANY
TOM

2. The same three letters, in the same order, will change each of the words below into new ones:

ZIT
RAT
NET
LEA

HINTS:
1. The three letters precede each word.
2. The three letters follow each word.

Answers:

1. The letters are BOT:

BOTTOM
BOTHER
BOTANY

2. The letters are HER:

ZITHER
RATHER
NETHER
LEATHER