You are asked to tutor a friend in algebra with adding and subtracting trinomials. create an example of how to add two trinomials and how to subtract two trinomials. come up with two trinomials and be sure to

Addign trinomials (2x+4xy+8z)+(8x+5xy+23z) all you have to do is combine the like terms 2x and 8x= 10x, 4xy+5xy=9xy, and 8z+23z=31z. so the simplified answer to adding the trinomials would be 10x+9xy+31z. 

Subtacting trinomials (4x+9y+3) - (-1+3x-2y) . 
When doing subtracting you still combine like terms but this time you change the sign before every term. If that is confusing, just pretend there is a negative 1 infront of parenthases and multiply that before you subtracts the two trinomials. so...
4x - 3x= x, 9y+2y=11y and 3+1=4. so simplified answer of the subtraction would be x+11y+4 

I hope this helped :) Good luck !