Help about function with if statement

I have problem with creating function. I don´t know how to use command function properly. Can you guys tell me where I was wrong it will be very helpfull

function [y]=task1(x)

if x>=9

       y = 15*(4*x)^(1/2)+10;
end

if (0<=x<9)

         y=10*x +10;
end

if (x<0) y=10;

end