Ed Miller Response Probability Question

[Megenoita]

This is from the 2+2 internet magazine article. Regarding a KJ hand, Ed Miller wrote the following calculation:

EV = (0.80x)(13) + (0.20y)(13) + (0.20x)(-2) + (0.80y)(-2) + (z)(-2)

Where does he get the (13) and (-2)?

Lost,M

[Lost Wages]

[ QUOTE ]
You are thus risking two bets to win thirteen -- the twelve in the pot and your opponent's river bet.

[/ QUOTE ]

-2 is what you lose when you lose, 13 is what you win when you win.

Lost Wages