What Goes Up

I have 4 corners. I have 4 sides.

All of my sides are the same length.

Who I am?

Think of a number

Step 1: Multiply it by 3

Step 2: Add 6

Step 3: Divide by 3

Step 4: Subtract the number chosen in step one from the answer in step 4.

What is the answer?

You can see me on trees. My body is round and yellow.

I am very healthy. You can squeeze me and drink me in summer.

I taste sour.

Who I am?

I am a pet. I like mice.

I have nine lives. I purr and meow.

Who I am?

I am the third planet from the sun. I orbited by one moon.

I am also called as the blue planet and the living planet.

Who am I?