Answer :

well first, convert everything to inches... that makes it a simple addition problem...

4 ft is 48 inches
3 ft and 1 inch is 37 inches

48 and 37 is 85 inches.
Since 1 ft equals 12 inches. you multiply 4 and 3 by 12. when you multiply them and add them together you get 84 inches. Then you add the 1 inch to 84 inches. 
AND YOU GET 85 INCHES. 

SO 4FT AND 3FT 1 INCH EQUALS 85 INCHES.