Four Days of the Week

Can you solve it?

E + E + E = 15

E + C = 8

C + E + B = 10

B + C * J = ????

I have 4 corners. I have 4 sides.

I have 2 long sides and 2 short sides.

Who I am?

What occurs:

Twice in a Week, Once in a Year!

But never in a Day?

My body is long. I am very healthy.

You can make juice from me. I wear an orange coat. 

I grow underground.

Who I am?