All that I can do for you is to give you some tips so that it would be easier for you to complete this work.
So, the first thing you should remember is that you have to make a programm which will accept as input two numbers and, of course floats to be more precise, which is totaly essential!
The next step is set up the input, suppose it would be 2.3 and 10.
Next thing, the program you make must be able to compute the area and divide the numbers of your results using the rate of grass cut/second.
Since we decided that it's 10 second'sm, the last thing you shoul do is just to turn seconds into minutes.
I am pretty sure it will help you to manage well!