in f(g(4))
firstly we calculate g(4)
g(4) will call g(1) + g(1) which will give (3+3) =6
now f(6)is called
step 1: f(6) calls f(4) + g(4) = f(4) + 6 = 7+ 6= 13(from step 2) which is the ANSWER
step 2: f(4) calls f(2) + g(2) = 1+6 = 7 (from step 4 & 3)
step 3:g(2) calls g(1) + g(1)=6
step 4:f(2) will return1 to f(4)