You aren't expected to do the exact calculations at the table. To build your ability to estimate the risk premium, you perform the exact calculations on many examples, and then notice patterns. For example, you might notice that the risk premium is low when you cover the pusher by a lot, even when it is the bubble, or that the risk premium increases on the bubble when a player with a short stack has already folded. You might notice the risk premium is never negative, even if you have the chance to knock someone out.

My program

ICM Explorer does the exact calculations, and computes the risk premium for you. This is the output for calling a small blind push with the stacks you give:

Fold: 2700 chips, 0.2524, SD: $14.56

Win: 6000 chips, 0.3604

Lose: 0 chips, 0

Tie: 3000 chips, 0.265

**Equity needed: 70.04%**
Chip odds: 45%

Risk premium: 25.04%

Chips gained by marginal call: 1502.34.

Ties count as 73.52% of a win.

SD of marginal call: $18.42.

If you want to check the calculation, you could take the values for folding, winning, and losing, and compute that the equity needed to call is (fold-lose)/(win-lose) = (.2524-0)/(.3604-0) = 0.7004. Then you subtract the chip odds, also calculated by (fold-lose)/(win-lose), with all outcomes evaluated in chips: (2700-0)/(6000-0) = 0.45. 0.7004-0.45 = 0.2504. I don't think you need to be able to build your own calculator to use one, though. It is better to focus your attention on what your opponent's range might be. The risk premium simplifies the estimate of the equity you need because you don't have to evaluate the equities from folding, winning, and losing.