Solution 2 :

(a) Input high voltage,

VIH = 0.8 + 0.7 - 0.5 = 1 v

     Input low voltage,

VIL = 0.7 + 0.7 - 0.5 = 0.9 v

(b) Output high voltage,

VOH = 5 - 0.7 - 0.7 = 3.6 v

     Output low voltage,

VOL = Vce(SAT) = 0.5 v

(c)                                               VTC