Consider the number xy where:
xy = 10 . x + y
x . y = 35
xy + 18 = yx
10.x + y + 18 = 10.y + x
10.x - x = 10.y - y - 18
9.x = 9.y - 18
x = y - 2
(y - 2) . y = 35
y^2 - 2y - 35 = 0
Using the Bhaskara formula:
y = 7 (the negative solution is discarded)
x = 7 - 2
x = 5
Response: the xy number is 57.
;-)
