Since both products cost the same each ($2), we can consider how many multiples of seven (six thermometers for each heat pack) would make up the 567 items sold. ($1134 total sales divided by $2 per item)
567/7 = 81. There were 81 heat packs sold.
6 * 81 = 486. There were 486 thermometers sold.
Checking our math: 81 + 486 = 567. 567 * $2 = $1134.