The interior angles in a regular polygon are 140 degrees. how many sides has the polygon?
it could be something to do with s=(n-2) x 180

Yes, it certainly could !  When you first noticed that formula in a book, or when it was given to you in class, did you also notice or learn what it means ?

It means
"The sum of all the interior angles in a polygon" = (number of sides - 2) x 180.

Triangle 3 sides ... (3 - 2) = 1 x 180 = 180° degrees ... 60° each if regular
Quadrilateral . 4 sides ... (4 - 2) = 2 x 180 = 360° degrees ... 90° each if regular
Pentagon 5 sides ... (5 - 2) = 3 x 180 = 540° degrees ... 108° each if regular
Hexagon 6 sides ... (6 - 2) = 4 x 180 = 720° degrees ... 120° each if regular
Sevenagon ... 7 sides ... (7 - 2) = 5 x 180 = 900° degrees ... 128 and 4/7 each if regular
Octagon 8 sides ... (8 - 2) = 6 x 180 = 1080° degrees ... 135° each if regular
Nonagon 9 sides ... (9 - 2) = 7 x 180 = 1260° degrees ... 140° each if regular