The exponential function is defined as y = a(1+r)^x, where "a" represents the original account and "r" the rate of growth or decay.
Then we have the following:
1) 22% grow
y = a( 1 + 22%/100 )^x = a(1.22)^x
So the solution is: 124(1.22)^x
2) 12% decay
y = a( 1 - 12%/100 )^x = a(0.88)^x
So the solution is: y = f(x) = 44(0.88)^x
3) 20% decay
y = a( 1 - 20%/100 )^x = a(0.8)^x
So the solution is: f(x) = 22(0.8)
4) 12% Groth
y = a( 1 + 12%/100 )^x = a(1.12)^x
So the solution is: f(x) = 42(1.12)^x