Question 287669
Hello, 
First let's find how much grass there is to cut by subtracting 1290 from 1600. 
That gives us 310 sq ft. 
Now divide 2 sq ft per minute into 310 sq ft. to give us:
155 seconds
Now if the yard is 1600 st then it would take:
800 seconds or 13 1/3 minutes.
The problem isn't totally clear what is to be cut.
RJ
www.math-unlock.com