The five days that I stayed in Tokyo in August were exceptionally hot.

英訳に間違いが有れば正してください。

滞在した八月の東京の五日間は非常に暑かった
The five days that I stayed in Tokyo in August were exceptionally hot.

ヒント
The five days

答え wereをwasにする

The five days that I stayed in Tokyo in August was exceptionally hot.

The ….daysは一度の期間として扱い単数で受ける