what colors do i have to to mix obtain brown?

Answer 1

Either
mix red, yellow, and blue; or
mix red and black, or
mix red yellow blue and black or
mix green and red or
mix blue and orange or
mix yellow and purple.

Answer 2

Any 2 opposite colors on the color wheel.

A standard color wheel has 6 colors, in an order similar to this:

RED
PURPLE
BLUE
GREEN
YELLOW
ORANGE

So the colors that make brown are:

purple + yellow
red + green
blue + orange

Answer 3

Red and green
Orange and black

If you mix two complementary (i.e., opposite on the color wheel)colors, you get grey.