You can work it out with a tape , a straight edge & a calculator but easier to look for a stamp on rear as "Et" followed by a number between 35 & 50 . width will be 8j . 8.5j or 9j I would assume
The offset will (should) be stamped on the rear of one of the spokes. Remove one front and one rear alloy and you will (should) see it. May need to clean the rear of the wheel first, for obvious reasons.