The sum of the real numbers x and y is 25. Their difference is 18. What is the value of xy ?
x+y =25 y = 25 -x
x-y = 18 sub in for y
x -(25-x) = 18
2x = 43
x = 21.5
y = 3.5 21.5 *3.5 = _________
+37165 
