Finding a variable in a equation using regression method

Please, I'm new to MATLAB and I want to know how to solve a problem.

I have two variables with 2000 values (I choose 10 to put here):

x = [ 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 ];

y = [-3.6621 7.32421 -1.831054 -1.831054 -7.32421 3.6621 -1.83105 0.00023 0.00847]

These variables are in the equation: y = K((e^(x/25)) − 1)

I have to use Ordinary least squares (linear regression) or Semilogarithmic plot to find the "K" with the informations above of x and y.

If I choose linear regression I can use these functions: fit, fittype,fitoptions.

Thanks!