Can anybody tell me the step by step?

I'm assuming you want to solve for each variable. There isn't much to do for your question.

We want x:

x + y = 12

Subtract y to get x alone.

x = 12-y

We want y:

x+y=12

Subtract x to get y alone.

y = 12-x

could

step-by-step explanation:

u send me a picture of ur work

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.