A trolley with apples is placed on a uniform plank XY of length $9.0$ m and weight $600$ N.

The plank rests on a single support at a distance of $3.0$ m from end X. The centre of the trolley is at a distance of $2.0$ m from end X.

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An empty trolley has a weight of $150$ N. One apple has a weight of $2$ N.

The plank is balanced horizontally. How many apples are in the trolley?