T(n) = 22 T(n/2) + C
T(n) = 24 T(n/22) + 4C + C
T(n) = 26 T(n/23) + 42C + 4C + C
T(n) = 28 T(n/24) + 43C+ 42C + 4C + C
and so on... (Now you will get a pattern)
Let n = 2k , Hence k = logn.
From the above pattern we can write
T(n) = 22k T(n/2k) + 4k-1C + 4k-2C + ..... + C
T(n) = 22k T(1) + (4k-1 + 4k-2 + .... + 1) C (G.P of K terms with initial term is 1)
T(n) = 22logn + 1*(4k - 1)/3 * C
T(n) = n2 + (22k -1) /3
T(n) = n2 + (n2 -1)/3
T(n) = O(n2)
This is the exact solution by substitution . :)
But these kind of questions should be directly solved using master's theorem.