Question 650070
Let the side of a square be 's'feet
Area of the square= s*s=s^2 feet
Now side increases by 4 feet, s+ 4
The area also increases by 64 feet
We get, 
 (s+4)^2= s^2 + 64  ...(1)
 Apply the formula (a+b)^2= a^2 +b^2+ 2*a*b
 s^2 + 4^2+ 2*s*4= s^2+ 64
s^2 on both the sides get cancelled
 4^2+ 8s= 64
 16+ 8s= 64
 We have to shift the variable on one side and the numbers on the other side of 'equal to'sign
 8s= 64- 16
 8s= 48
  s= 48/8 ( here 48 is divided by 8 because on the other side of 'equal to' sign 8 was multiplied to s)
  s=6