This seems an exponential function.
Once you state that the function is exponential you can write is this form:
f(x) = A * b^x.
Then you need the y-intercept (i.e. x = 0) to find A
f(0) = A * b^0 = A
Once you have A, you can use the ordered pair (3,1) to find b
f(1) = A*b^2 = A*b = 3 => b = 3/A.
With that procedure you can find the function that represents the given graph.
Suppse the y-intercep is 0.1
Then f(0) = A = 0.1
And b = 3 / A = 3/0.1 = 30
And the function is f(x) = 0.1* 30^x
