The Transaction Journal shows how the adjustment was made.
The cost of the Sprinkler Heads was $.75, and they *reduced* by 5, for a total of $3.75. Assets live on the *Debit* side, so when the Inventory Asset account **decreases**, it shows this on the *Credit* side.
The cost of the Sprinkler Pipes was $2.50, and they *increased* by 4, for a total of $10.00. Assets live on the *Debit* side, so when the Inventory Asset account **increases**, it shows this on the *Debit* side.
COGS is an Expense account, which also lives on the Debit side. It increases on the left and decreases on the right.