Solution-
An intermediate good is a product used to produce a final good or finished product. These goods are sold between industries for resale or the production of other goods.
As toy plane and doll house are the finished product, they can't be the intermediate goods. But, in case of the plastic sheets, they are used for the manufacturing of the end products.
∴ In mr.Gareth's toy-manufacturing company, plastic sheet is an intermediate good.