Simplify the following text for a Grade 9 native English-speaking person.
Original: Dalrymple was bitterly disappointed that it was Captain Cook and not him who was appointed commander of the expedition which eventually led in 1770 to the British encounter and charting of the eastern coastline of Australia .
Simplified: Dalrymple was angry that it was Captain Cook and not him who was put in charge of the expedition which led in 1770 to the discovery of the east coast of Australia .