I often hear things like "when we want to call a 3-bet, we just need to lose less than our pre-flop raise size by calling, because if we fold, then we lose our entire raise."

My question (by example) is:

Suppose that we open to 3 big blinds, and get 3-bet to 10 big blinds. We need to call 7 more big blinds.

Suppose that our opponent will continuation bet 100% of the time, and that we will fold the flop 80% of the time, and the other 20%, we will win an unknown amount X.

We want to set up an indifference equation to solve for the value of X.

The value of raise/folding is -3 big blinds, and (assuming our post-flop strategy and outcome above) the value of raise/calling is: (2/10)*(X) + (8/10)(-10), correct?

Thus, the indifference equation should be:

(2/10)(X) + (8/10)(-10) = - 3

Would somebody confirm this is the case?