BA2 Question

Hi All, I am having a mental block. In chapter 7 of standard costing & variance analysis (illustration 2) the following has been detailed: direct materials: 81kg x $7 per kg = $67 per unit direct labour: 97 hours x $8 per hour = $776 per unit variable overhead: 97 hours x $3 per hour = $291 per unit as I said, mental block going on here, but how did they calculate that their variable overhead was $3 per hour? Many thanks in advance!!