J need function that calculate formula in infix notation. For exempele function that takes string as argument and return an float as value of that formula. J make function that calculate postfix formula but it is not help me to solve problem.

Nobody will write code for you. If you have already written a postfix parsing function you will find infix easy. Try and post what you have done upto now. We will help you correct errors.

Also you are typing J instread of I.

J need

J make

Correct that.