The average of the ages of Sushanth, Krish and Rishi is 43 years and the average of the ages of Sushanth, Rishi and Rohit is 49 years. If Rohit is 54 years old, what is Krish's age ?

Let present ages of Sushanth = w, Krish = x, Rishi = y and Rohit = z , then
w + x + y = 43 x 3 = 129 ---(i) and
w + y + z = 49 x 3 = 147 ---(ii)
Subtracting (i) from (ii), (w+y+z) - (w+x+y) = 147 - 129 , z - x = 18 ---(iii)
Given Rohit's age=z=54, so from (iii), x = 54 - 18 = 36.
Therefore, Krish age is 36 years.