First we determine the value of d, how many kilometres travelled. To do this, we can use the formula d = v*t, where d is distance, v is speed, and t is time. Taking into account that 45 minutes = 3/4 hour, and adding the two legs of the journey, we find, d = 80*3 + 40*3/4 = 240 + 30 = 270 km.
Next, we use another version of the formula, v = d/t. The time (t) of the whole trip was
3 + 3/4 = 12/4 + 3/4 = 15/4, and so the average speed (v) is given by
v = d/t = 270/(15/4) = 270*4/15 = 72 kph.
Correct answer is (C) - d=270; v=72