what the hell - growing annuity

Guys

I am doing an exercise (I don't know for how long now) that I just can't understand, worst, it's quite simple.

opportunity cost for equity holders = 10%

Stock C is expected to pay a dividend of $5 next year. Thereafter, dividend growth is expected to be 20% a year for five years (i.e., years 2 through 6) and zero thereafter. PV?
The guy gave us the solution:

(1) PV growing annuity: PV = 5 [ (1/ 0.10 − 0.20) − (1.20^5 /(0.10 − 0.20) × 1.105^5) ] = 27.25

(2)PV perpetuity: 5 * (1.20^5/0.10/1.105=77.25

PC = 27.25 + 77.25 = $104.50

How on earth does he find 27.25? In my calculations ( 0.10-0.20)= - 0.1
I'm always stuck with a negative number. I don't get it